PHOTOGRAPHY  WITH  EMULSIONS: 


A TREATISE  ON 

THE  THEORY  AND  P^ACTIGAL  WORKING  OF 

GELATINE 

AND 

COLLODION 


Emulsion  Processes, 


— BY — 

CAPTAIN  W.  DE  ¥.  ABNEY,  B,  E,,  F.  B.  S. 


NEW  YORK: 

SCOVILL  MANUFACTURING  CO., 

W.  IRVING  ADAMS,  Agent. 


1882. 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/photographywithe00abne_0 


CONTENTS 


Aceto  Gelatine  Emulsions  

PAGE 

220 

Albumen  Beer  „ 

,,,  ,,, 

88 

Albumen,  Stock  

. . • • 

79 

Alkaline  Development  of  Gelatine  Elates 

. . . . . . 

188 

Alkaline  Development,  Theory  of 

9fa  ... 

15 

Alum  Bath 

...  . . . 

209 

Ammonia,  Gelatine  Emulsion  with  

o ♦ • . . . 

162 

Ammonia  Process,  Comparison  of,  with  Boiling 
Gelatine  Emulsion  

Process  in 

128 

Appendix  ...  ...  ...  

233 

Backing  for  Gelatine  Plates  

239 

Backing  for  Plates 

84 

Beechey’s  Process 

57 

Beer  Preservative 

85 

Bennett’s  Process  ... 

149 

Black  Spots  on  Development  

108 

Blanchard  Brush 

...  ... 

81 

Blisters  in  Films 

108, 

227 

Boiling  Gelatine  Emulsion  

...  . . . 

142 

Brush,  Blanchard 

...  ... 

*81 

Burton’s  Process  ... 



159 

Carey  Lea’s  Preservative  ...  

87 

Carey  Lea’s  Processes  

55 

Chardon’s,  Collodion  Emulsion  Process 



59 

Chloride  Emulsion  in  Gelatine  ... 



213 

Chloride  in  Gelatine  Emulsion 

126 

Chlor-Xodo-Bromide  Collodion  Process 

64 

Chloro-Bromide  Collodion  Emulsion 

55 

Citric  Acid  with  the  Developer 

. 

199 

IV 


CONTEXTS. 


PAGK 


Cleaning  Plates  for  Gelatine  Emulsion  ...  182 

Coating  the  Plate  with  Collodion  Emulsion  ...  81 

Coffee  Preservative  88 

Cold  Emulsifying  Process  with  Ammonia  ...  ...  ...  170 

Collodion  Emulsions  ...  34 

Collodion  Emulsion,  Preparation  of  ...  ...  ...  ...  45 

„ „ Mixing  48 

,,  ,,  Ripening  of  ...  ...  ...  ...  49 

,,  „ Pellicle  for  ...  ...  ...  ...  52 

„ „ Preparation  of  Plates  77 

Collodion,  Plain,  for  Emulsions  ...  ...  ...  ...  ...  34  /■ 

Collodio- Albumen  Process ...  ...  ...  ...  75 

Collodio-Bromide  with  Excess  of  Bromide  ...  ...  ...  72 

Collodio-Bromo-Chloride  Emulsion  ...  ...  ...  ...  107 

Collodio-Chloride  Process...  ...  ...  ...  ...  ...  104 

Collodio-Emulsion  Preservatives^...  ...  ...  ...  ...  85 

Comparison  ot  Ammonia  Process  with  Boiling  Process  in 
Gelatine  Emulsions  ...  ...  ...  ...  ...  ...  128 

Composition  of  the  Developable  Image...  ...  ...  ...  4 

Cooking  and  Washing  Gelatine  Emulsion  ...  ..  ...  143 

Cool  Emulsification  without  Ammonia  ...  ...  ...  ...  181 

Cooper’s  Reliable  Collodio-Bromide  Process  ...  ...  ..  67 

Cotesworth’s  Method  of  Emulsification...  ...  ...  ...  181 

Cotton-wool  for  Filtering ...  ...  ...  ...  ...  ...  80 

Cowan’s  Drying- Cupboard  ...  ...  ...  ...  ...  25 

Cowan’s  Process  ...  170 

Crape  Markings  in  the  Film  108 

Cure  for  Fog  11 


Dark-Room  and  Fittings , 

,,  „ Illumination  of 

,,  ,,  Lanterns  for 

Dawson’s  Process  ... 

Defects  in  Collodion  Emulsion  Plates 
,,  in  Gelatine  Plates 


Developer,  Chardon’s 

3 3 

Brooks 

33 

Edwards’ 

33 

Ferrous  Oxalate 

33 

Ferrous  Citrate 

33 

Ferrous-Citro  Oxalate 

33 

for  Gelatinized  Paper.. 

33 

Blender  son’s 

33 

liydrokinone  ... 

33 

Hydrosulphite... 

20 

27 

32 

62 

108 

224 

92 

93 
194 


18,  235,  236 


236 

237 
217 
197 
237 

9 


CONTEXTS. 


Developer,  Nelson’s  

„ Weak  Alkaline 

„ Wratten  and  Waimvright’s 

Developing,  Screen  for  

Development,  Alkaline,  Theory  of 

„ of  Collodion  Emulsion  Plates*  .. 

,,  of  Gelatine  Plates  ... 

„ with  Potassium  Ferrocyanide 

Dissolving  the  Emulsion 

Draining  „ „ 

Drying- Cupboards 

,,  Gelatine  Plates  .- 

,,  Markings  in  Collodion  Emulsion 

Eder’s  Emulsion  with  Ammonia  ...  

Eder  on  Gelatine  and  Gelatine  Chloride  Emulsion 
Elsden  on  Gelatine... 

Emulsions,  Collodion 

Emulsions,  Fog  in 

Emulsion,  Granular  

Emulsion,  Preparation  of  a Collodion  ... 
England’s  Drying- Cupboard  

Fatty  Matter  in  Gelatine 

Ferrous  Citrate  Developer  

Ferrous  Citro-Oxalate  Developer  

Ferrous  Oxalate  Developer  ...  

Ferrous  Oxalate  Development  of  Gelatine  Plates 

Fixing  Gelatine  Negatives 

„ Solutions  for  Collodion  Emulsions 

Fog,  Cure  for  

„ General 

,,  Green 

„ in  Collodion  Emulsion  

„ in  Emulsions 

„ Red 

Frilling  

Gelatine 

Gelatine  Emulsion,  Cooking  and  Washing 

» » Keeping  

» » Mixing 

Gelatine  Plates,  Drying 

Gelatine,  W ater  Absorbed  by 

,,  Fatty  Matter  in 


V 

PAGE 

• • • 

198 

99 

• • 1 

198 

31 

• • • 

15 

• • • 

91 

188, 

200 

c • • 

197 

... 

147 

147 

21,  24,  25 

. , • 

187 

... 

110 

162 

133 

133 

• • • 

34 

5 

... 

231 

... 

45 

22 

135 

... 

236 

237 

18,  235, 

236 

... 

200 

... 

209 

t#t 

101 

11 

228 

227 

109 

• • • 

o 

227 

... 

224 

132 

... 

143 

247 

. , . 

140 

187 

134 

... 

135 

CONTENTS. 


VI 


PAGE 


Gelatinized  Paper...  

•••  ••• 

... 

215 

Gelatino-Bromo-Iodide  Emulsion 

•••  ••• 

... 

137 

Gelatino- Chloride  Emulsion 

...  ••• 

... 

212 

Glycerine,  Gelatino -Bromide  Emulsion  made  with 

• •• 

175 

Granular  Emulsion  

. . . • • • 

... 

231 

Green  Fog 

...  ... 

227 

Gum  Guiacum  „ 



... 

90 

Hot  Weather,  Making  Emulsion  in 



... 

172 

Hydrokinone  Developer 

... 

237 

Illumination  of  Dark-Room 



... 

27 

Image,  Composition  of  Developable 

... 

... 

4 

„ Flatness  of 

...  ... 

... 

229 

„ Too  great  Density  of 

... 

... 

229 

Impurities  in  Bromides  

...  ... 

... 

6 

Insensitive  Patches  in  Collodion  Emulsion  Films 

... 

108 

Intensification  . . 

M#  ... 

... 

93 

Intensifies  England’s 

...  ,,, 

... 

206 

,,  Edward’s  

, # # . 

... 

207 

„ Uranium  

... 

207 

Intensifies  for  Gelatine  Plates  ... 

. . . ... 

. . . 

106 

Intensifying  Gelatine  Negatives  ... 

...  ... 

... 

204 

Intensifying  Solutions  

... 

238 

Introductory  Remarks  on  Gelatine  Emulsions... 

... 

111 

Iodide  in  Gelatine  Emulsions 



... 

121 

Konarzewski’s  Emulsion 



... 

223 

Lanterns  for  Dark-Room 

32 

Levelling  Shelf  

184 

Liebig’s  Condenser  



... 

233 

Mixing  Gelatine  Emulsion 

140 

Mixture  of  Haloids  

... 

241 

Moist  Collodion  Emulsion  Process 

...  ... 

. . . 

102 

Molecular  State  of  Silver  Bromide 

...  ... 

• • • 

3 

Monckhoven’s  Drying-Cupboard... 

...  ... 

... 

24 

Monckhoven’s  Process  



178 

Nitric  Acid  in  the  Developer 

199 

Note  Book 



... 

246 

Packing  Plates  



... 

242 

Paget  Prize  Gelatine  Emulsion  ... 

...  ... 

... 

152 

Papers,  Gelatinized  

... 

... 

215 

CONTENTS. 


Yll 


Peeling  of  Films  off  the  Plate  

109 

Pellicle,  Preparation  of,  for  Collodion  Emulsion 

52 

Plate,  Coating,  with  Collodion  Emulsion 

81 

Plates,  Backing  for 

84: 

„ Defects  in  Collodion  Emulsion 

108' 

,,  Packing  

242 

„ Preparation  of,  with  Collodion  Emulsion 

77 

Preliminary  Considerations  

1 

Preparation  of  Gelatine  Plates  

182 

Preservatives  ...u  ..  

85,  86 

„ Albumen  Beer  

• • • 

88 

„ Carey  Lea’s 

87 

„ Coffee...  ..  

88 

„ Tannin  

87 

„ with  Collodion  Emulsions 

85 

,,  Wortley’s  

89 

Process,  Bennett’s 

149 

„ Beechey’s  

57 

„ Burton’s 

159 

„ Carey  Lea’s  ...  

55 

,,  Chardon’s  

• • c 

59 

„ Collodio-Albumen  

75 

,,  Collodion-Bromide,  with  Excess  of  Bromide... 

72 

„ Cooper’s  Collodio-Bromide  

67 

„ Cowan’s  ...  

170 

„ Dawson’s  

62 

„ Hardwich’s  

... 

...37,38 

„ Lohse’s  

248 

,,  Moist  Collodion  Emulsion  

102 

„ Monckhoven’s 

178 

,,  Simpson’s  

41 

,,  Slew  Collodion  Emulsion  

239 

,,  Slow  Gelatine  Emulsion  

239 

Pyroxyline 

37 

,,  Taylor  on  

42 

„ Warnerke’s  ...  

40 

Red  Fog  ...  

227 

Residues  

• • • 

240 

Reversed  Method  of  Mixing  ...  

... 

141 

Scales  and  Weights 

138 

Screen  for  Developing 

31 

Sensitiveness  in  Gelatine  Emulsions,  Cause  of... 

• • • 

114 

„ Increase  of  in  Gelatine  Emulsion  by  Keeping 

118 

Till 


CONTENTS. 


Sensitiveness,  Range  of,  of  Silver*  Iodide 
„ „ „ Bromide 

„ ,,  „ Chloride 


4 

4 

4 


Sensitometers 

• • • 9 • • 

244 

Shelf,  Levelling  

... 

184 

Shelves,  Level  Cupboard 

186 

Silver  Lactate  

•••  • •• 

68 

Silver  Nitrate  with  Gelatine  Plates  



248 

Sodium  Hyposulphite,  Action  of,  in  Developer 
,,  ,,  in  the  Developer 

...  ,,, 

19 

„ . . #M 

202 

Solvents,  Evaporating  of  Collodion  Emulsions.. % 

• - ... 

50 

Spots,  Dull 

...  ... 

232 

„ Opaque  ...  

... 

231 

„ Semi-transparent 

M. 

231 

Substrata  

...  ... 

183 

Substratum,  Gelatine  

...  ... 

78 

,,  Albumen  

78 

!,  79 

,,  India- rubber...  

...  ... 

81 

Sulphite  of  Soda  in  the  Developer 

199, 

248 

Tannin  Preservative  ...  ...  ..  ... 

87 

Transparent  Films,  Thin  ... 

...  ... 

108 

Trays  



245 

Varnishing  the  Negative 



210 

Vogel’s  Emulsion 



220 

Warnerke’s  Process 

242 

Washing  Collodion  Emulsion  

...  ... 

50 

,,  Gelatine  Emulsion  

144, 

145 

Water  in  Dark-Room  

••• 

21 

Windows,  Coloured  Medium  for 

...  ••• 

240 

Wortley’s  Preservative  



89 

PHOTOGRAPHY  WITH  EMULSION'S. 


CHAPTER  I. 

PRELIMINARY  CONSIDERATIONS. 

The  term  emulsion  is  derived  from  the  Latin  word 
u emulgere,”  to  milk  out,  and  the  definition  of  it  as  found 
in  the  dictionary  is,  u any  milk-like  mixture  prepared  by 
uniting  oil  and  water  by  means  of  another  substance.” 
For  our  photographic  technology  this  is  hardly  a correct 
definition,  for  by  it  we  mean  a sensitive  salt  of  silver  in 
very  minute  division,  held  in  suspension  in  some  viscous 
body,  such  as  gelatine,  or,  more  commonly,  collodion. 

An  emulsion  in  its  simplest  form  may  be  considered 
to  be  simply  a pure  silver  haloid  held  in  suspension  in 
collodion  or  gelatine,  and  so  well  prepared  that  when  a 
plate  is  coated  with  it,  a homogeneous  film  results ; a 
film  which,  in  fact,  is  at  least  equal  in  sensitiveness  and 
in  physical  qualities  to  any  which  can  be  prepared  by  any 
other  process. 

Emulsion  processes  are  divided  into  two  classes  : one 
in  which  the  emulsion  is  made  up  and  used  without  any 
preliminary  extraction  of  the  soluble  salts  which  are 
necessarily  present  in  their  manufacture,  owing  to  the 


2 


PRELIMINARY  CONSIDERATIONS. 


double  decomposition  of  the  salts  employed,  &c.,  and  tlie 
silver  nitrate  ; and  the  other  where  these  soluble  salts  are 
extracted.  In  the  first  process  the  plates  are  washed 
after  coating,  and  is  usually  confined  to  collodion  emul- 
sions ; whilst  in  the  second  they  are  coated,  and  generally 
left  to  dry  spontaneously. 

We  may  say  that  all  emulsions  at  present  in  vogue  may 
be  considered  to  be  simply  bromide  of  silver,  since 
it  is  the  basis  on  which  all  alterations  by  the  addition  of 
iodide  or  chloride  are  to  be  made.  It  will  be  seen  in  the 
context  that  these  additions  are  not  unimportant  as  re- 
gards the  range  of  sensitiveness. 

The  universal  mode  of  production  in  emulsion  is  to 
dissolve  certain  soluble  bromides  (such  as  potassium 
bromide)  in  the  collodion  or  in  a gelatine  solution,  and 
then  to  gradually  pour  a solution  of  silver  nitrate 
dissolved  in  alcohol  and  water  in  the  first  case,  or  in  water 
alone  in  the  second,  into  the  viscous  fluid,  by  which 
means  solid  bromide  of  silver  is  formed,  together  with  a 
soluble  nitrate  (such  as  potassium  nitrate).  It  is  this 
latter  soluble  product  which  in  washed  emulsions  is 
removed,  since,  if  a film  be  left  to  dry  without  eliminating 
it,  crystallization  sets  up,  and  the  surface  of  the  coated 
plate  is  spoilt.  Silver  chloride  is  readily  emulsified  in 
the  same  way,  subsituting  a soluble  chloride  (such  as  of 
sodium)  for  the  soluble  bromide.  Silver  iodide  is  also 
easily  formed  into  an  emulsion  in  gelatine,  but  it  is  formed 
with  much  more  difficulty  in  collodion.  We  give  the 
chemical  equation  for  the  formation  of  silver  bromide. 

Potassium  Bromide  and  Silver  Nitrate  give  Silver  Bromide  and  Potassium  Nitrate 

.KBr  + AgNOs  = AgBr  KN03 

Bromide  of  silver  maybe  produced  in  several  molecular 
states,  all  of  which  have  different  degrees  of  sensitiveness. 
When  we  say  different  molecular  states,  we  mean  that 
the  silver  bromide  has  precisely  the  same  chemical  com- 
position, but  that  it  is  altered  physically,  the  molecules 


PRELIMINARY  CONSIDERATIONS. 


3 


being  larger  in  some  cases  than  others ; the  tangible 
molecule  being  built  up  of  a greater  or  less  number  of 
primary  molecules,  according  to  the  rapidity  of  the  for- 
mation of  the  solid,  and  its  subsequent  treatment  by  heat, 
ammonia,  &c.  Thus,  it  is  known  that  transmitted  light,  as 
seen  through  a film,  may  appear  of  a ruby,  orange,  green, 
purple,  or  grey  colour ; and  of  these,  three  seem  to  be 
different  states  of  molecular  aggregation — viz.,  ruby, 
green,  and  grey  ; the  others  are  probably  mixtures  of  one 
or  more  of  the  three.  We  must  assume  that  the  reader  is 
aware  what  a spectrum  is.  By  exposing  any  of  these 
modifications  to  its  action  we  find  that  the  range  of  sensi- 
tiveness to  the  different  coloured  rays  is  varied.  Thus  the 

PRISMATIC  SPECTRUM. 


H G F E D B A 


ULJflA  - V/OLET  VIOLET  BLUE  CREEN  YELLOW  RED  INFRA-RED 


Fig.  1. 

ruby  and  orange  modification  is  sensitive  to  the  ultra 
violet,  the  violet,  and  blue  rays,  and  a little  in  the  green ; 
the  grey  blue  is  sensitive  to  the  same  rays,  but  more 
strongly  in  the  green,  whilst  it  is  able  to  be  impressed  by 
the  yellow  and  by  the  red  rays ; the  green  modification, 
when  in  collodion,  is  sensitive  to  the  ultra  violet ; the  blue, 
very  slightly  to  the  green,  and  much  more  so  to  the  red, 
and  infra  red  region,  i.e.:  those  dark  rays  which  are  mis- 
called the  heat  rays. 

In  collodion  emulsion  the  ruby  and  orange  form  of 
bromide  is  that  most  sought  after,  whilst  in  gelatine  emul- 
sion the  form  which  is  supposed  to  give  the  most  sensi- 
tive films  is  the  blue  grey  form ; though  for  our  own 
part  we  consider  that  a tinge  of  yellow  is  essential  to  get 
the  highest  sensitiveness.  The  reason  for  selecting  these 
forms  we  shall  touch  upon  by-and-bye. 


4 


PRELIMINARY  CONSIDERATIONS. 


Iodide  of  silver  in  its  pure  state  is  sensitive  only  to  the 
ultra  violet,  the  violet,  and  the  blue  rays,  and  just  to  the 
margin  of  in  green,  and  it  may  well  be  supposed  that  by 
adding  iodide  to  the  bromide  some  modification  of  the 
range  of  spectral  sensitiveness  must  be  found.  Such  is 
the  case,  and  it  is  more  marked  in  gelatine  emulsion,  in 
which,  were  no  jodide  added,  the  emulsion  would  take  the 
blue  grey  state. 

If  we  add  4 per  cent  of  iodide  of  silver  to  the  bromide 
in  a gelatine  plate,  the  sensitiveness  is  diminished  in  the 
red  rays,  and  the  yellow  rays  will  not  impress  themselves, 
except  by  very  prolonged  exposure.  If  we  add  8 per 
cent.,  the  green  rays  are  with  the  greatest  difficulty  im- 
pressed, where  with  12  per  cent,  the  rays  which  can  im- 
press themselves  are  confined  to  the  part  of  the  spectrum 
to  which  the  iodide  per  se  is  sensitive. 

Chloride  of  silver  modifies  the  photographic  qualities 
of  the  bromide  but  little,  and  since  it  is  but  rarely  used 
in  any  quantity,  we  need  not  consider  it. 

Chemical  Composition  of  the  Developable  Image. — Evi- 
dence of  the  most  unmistakable  character  points  to 
the  chemical  theory  of  the  formation  of  the  photographic 
image — evidence  so  strong,  and  so  well  known,  that  it 
would  be  out  of  place  to  record  it  here.  Briefly  we  may 
say  that  the  action  of  light  on  a silver  haloid  seems  to  be 
to  reduce  it  to  a simpler  type,  which  we  may  call  the  sub- 
lialoid.  Thus 

Silver  Bromide  gives  Silver  Sub-Bromide  and  Bromine. 

Ag  Br  > = AgiBr  -f-  Br. 

If  any  reader  will  not  admit  it,  he  should  read  all  the 
various  evidence  that  has  been  adduced  since  the  time 
when  Scheele  first  made  his  experiments  with  silver 
chloride,  and  we  doubt  if  he  can  remain  unconvinced,  more 
particularly  in  regard  to  the  visible  image  formed  on  the 
bromide  and  chloride.  It  is  a pertinent  question  to  put, 
as  to  whether  the  visible  and  the  invisible  (or  developable) 
image  are  of  the  same  nature ; which  may  be  answered 


PRELIMINARY  CONSIDERATIONS- 


5 


"by  another  question  : Can  the  line  be  drawn  where  the 
image  is  invisible  ? If  so,  what  is  the  boundary  between 
the  two  ? If  we  admit  the  theory  of  the  formation  of  the 
visible  image,  it  seems  hardly  logical  to  deny  a similar 
formation  for  the  invisible  or  photographic  image.  It  is 
quite  possible  that  beings  with  more  acute  sight  than  our- 
selves might  be  able  to  see  the  image  which  we  cannot, 
as  we  know  certain  insects  can  hear  sounds  which  do  not 
affect  our  auditory  nerves.  Coloured  particles  are  visible, 
when  put  together  en  masse , but  if  only  a few  coloured 
particles  are  present  in  a mass  of  colourless  particles,  it  is 
quite  certain  that  they  may  remain  undetected. 

If  we  may,  then,  be  allowed  to  beg  the  question,  or 
rather  to  assume  that  silver  bromide  is  reduced  by  light  to 
the  sub-bromide  as  indicated,  the  following  paragraph 
will  be  understood. 

The  Cause  and  Cure  of  Fog  in  Emulsions . — Every  student 
in  emulsion  work  has  found,  and  will  find,  that  the  chief 
obstacle  that  he  has  to  overcome  is  the  tendency  for  the 
plates  prepared  with  it  to  fog  on  development,  and  it  has 
taken  a great  deal  of  experimental  work  to  enable  it  to  be 
overcome.  The  reason  of  the  fog-giving  emulsion  has 
been  obscure ; but  the  writer  ventures  to  think  that  the 
recent  researches  that  have  been  made  on  the  subject 
have  explained  in  a great  measure,  if  not  entirely,  its 
raison  d'etre,  and,  in  spite  of  being  tedious,  or  of  being 
told  that  the  reader  knows  all  about  it,  a summary  ot 
what  is  known  of  the  matter  is  appended. 

Setting  aside  the  collodion  or  gelatine  from  the  question, 
and  merely  taking  into  consideration  the  sensitive  salts 
employed,  we  may  arrive  at  very  definite  results.  It  has 
been  asserted  that  a neutral  combination  between  two 
substances  can  never  take  place ; for  example,  if  we  mix 
potassium  chloride  with  silver  nitrate  we  shall  never  be 
able  to  get  pure  silver  chloride,  however  much  we  may 
wash  it — that  either  the  soluble  potassium  or  silver  salt 
will  always  be  in  excess,  though  in  the  minutest  quan- 


6 


PRELIMINARY  CONSIDERATIONS. 


tities.  This  certainly  is  the  case  theoretically,  because 
do  what  you  will,  and  wash  as  long  as  you  like,  there 
still  must  be  some  infinitely  small  part  of  the  soluble  salt 
left  behind.  Now,  for  ordinary  chemical  reactions,  where 
the  products  of  these  combinations  have  to  be  weighed, 
the  residual  impurity  may  be  inappreciable,  being  so 
infinitesimal  that  no  balance  yet  constructed  can  show 
them.  Though  a balance  may  be  inoperative,  yet,  as  is 
well  known,  light  is  able  to  show  us  impurities  in  a sub- 
stance which  may  not  be  one-millionth  part  ot  a grain  in 
weight.  By  passing  the  light  from  the  heated  vapours 
of  the  substance  and  its  impurity  through  a prism,  and 
noting  its  spectrum,  we  may  be  able  to  detect  the 
latter. 

The  spectroscope  will  not  tell  us  at  present,  however, 
whether  the  silver  or  potassium  is  present  as  nitrate, 
chloride,  bromide,  oxide,  &c. 

The  question  now  arises,  is  it  possible  to  detect  this  ? 
Is  it  possible,  for  instance,  to  say  whether  any  infinite- 
simal quantity  of  oxide  be  present  ? In  the  majority  of 
cases  the  question  would  be  an  open  one  ; but  where  we 
are  dealing  with  silver  salts  which  are  sensitive  to  light, 
and  which  are  amenable  to  development,  we  think  we  can 
give  an  affirmative  answer.  Sometimes,  however,  the  im- 
purities in  the  bromides  can  be  shown  by  weighing.  F or, 
in  a paper  read  before  the  Photographic  Society  of  Great 
Britain  on  the  8th  of  February,  1876,  Mr.  Warnerke 
stated  that  on  testing  the  different  bromides,  he  found 
that  considerable  variation  from  the  theoretical  quantities 
necessary  to  combine  with  silver  nitrate  was  observable. 
Thus  he  found  that  one  grain  sf  silver  nitrate  requires 

Of  potassium  bromide  1-35  grains,  theoretically,  1-429  grains, 

Of  ammonium  bromide  1-80  „ ,,  1-78  ,, 

Of  cadmium  bromide  1-005  „ „ -885  „ 

Of  zinc  bromide  1*43  „ „ 1*59  „ 

The  cadmium  salt,  he  states,  was  not  anhydrous,  there- 
fore this  may  account  for  one  discrepancy ; the  potassium 


PRELIMINARY  CONSIDERATIONS. 


7 


and  zinc  point  to  the  presence  of  oxide,  whilst  the  am- 
monium seems  to  indicate  the  presence  of  free  halogen.  Be 
this  as  it  may,  a careful  experimenter  has  found  these  dis- 
crepancies. 

Let  us  see  how  potassium  bromide  may  be  contaminated 
in  its  preparation.  We  find  that  the  mother  liquor  from 
the  sea  water  brine  is  treated  with  chlorine,  and  that  this 
takes  the  place  of  the  bromine  in  combination  with  the 
magnesium ; the  yellow  liquid  is  agitated  with  ether, 
which  takes  up  the  bromine,  and  this  ethereal  solution  is 
treated  with  potash  in  solution.  The  bromine  forms  the 
bromate  and  bromide  of  the  alkali,  and  when  the  alkali  is 
nearly  saturated,  it  is  decanted  off  and  further  treated.  Now, 
from  what  we  have  said  before,  it  is  more  than  probable 
that  the  bromide  is  contaminated  with  the  alkali,  however 
well  it  may  be  separated  : the  traces  of  alkali  may  even  be 
so  small  as  to  be  undetected  by  litmus  paper. 

Again,  the  bromides  of  the  alkaline  metals  are  prepared 
by  acting  on  the  alkalies  with  an  excess  of  bromine,  a 
similar  reaction  to  that  above  taking  place.  The  bromate 
is  decomposed  by  ignition,  and  this  heating  alone  tends 
to  decompose  the  bromide,  in  which  case  we  should  have 
the  oxide  of  the  alkali  left  behind.  In  good  preparations 
it  would  be  excessively  small,  but  still  sufficient,  for  the 
purpose  we  shall  indicate  presently. 

The  bromides  of  the  metals  may  be  similarly  contami- 
nated. Take  zinc  as  an  example ; the  metal  is  easily 
oxidized,  and  the  zinc  oxide  is  soluble  in  zinc  bromide, 
as  it  is  in  the  chloride.  In  all  these  cases,  then,  it  is 
possible  we  may  have  traces  of  oxide  with  the  bromide. 
Again,  there  are  some  metals  which  form  two  bromides,  as 
that  of  copper ; and  experience  shows  that  it  is  very  hard 
to  get  the  compound  fully  saturated  with  bromine  without 
having  part  of  it  in  the  less  saturated  state. 

If  such  bromides,  contaminated  with  the  oxide,  or  con- 
taining the  lower  combination  of  bromine,  be  brought  in 
contact  with  silver  nitrate,  we  shall  have  two  separate 


8 


PRELIMINARY  CONSIDERATIONS. 


reactions  to  consider.  In  the  case  of  the  oxide  contamina- 
tion, when  silver  nitrate  is  in  excess,  we  shall  have — 

Potassium  Bromide,  Potassium  Oxide,  and  Silver  Nitrate 

xKBr  -f  KoO  + (x  -j-  2)AgN03 

give  Silver  Bromide,  Silver  Oxide,  and  Potassium  Nitrate 

= #AgBr  -{-  AgsO  -J-  (x  ~\~  2)KNOs 

Or,  besides  the  silver  bromide,  we  shall  have  silver  oxide 
formed. 

We  have  seen  that  we  may  have  oxides  and  sub- 
bromides contaminating  the  bromides,  and  in  a similar 
way  we  may  have  oxides  and  sub-chlorides  contaminating 
the  chloride.  In  a communication  to  the  Philosophical 
Magazine , which  was  reprinted  in  the  photographic 
journals,  the  writer  showed  that  it  was  possible  to  deve- 
lop an  image  on  a film  never  exposed  to  light,  but  which 
was  in  contact  with  a film  (during  the  operation  of 
development)  on  which  an  invisible  image  had  been  im- 
pressed. The  explanation  there  offered  seems  every  way 
to  meet  the  requirements  of  the  case,  which  is,  that 
where  a nucleus,  if  it  may  so  be  termed,  exists,  there  the 
silver  from  the  adjacent  bromide  during  development  will 
be  deposited  in  preference  to  any  other  part  of  the  film. 
Such  a nucleus  is  found  in  the  silver  sub-bromide  or  sub- 
chloride obtained  by  exposing  a plate  to  light.  However 
produced,  we  may  assume  it  will  act  in  a similar  manner. 

The  case  of  the  oxide  is  not  so  clear ; but  a little 
experiment  will  throw  light  on  it.  Prepare  silver  oxide 
as  an  emulsion  in  collodion ; dissolve  (say)  6 grains  of 
silver  nitrate  in  an  ounce  of  plain  collodion,  and  add  to 
it  two  grains  of  potash  in  alcohol.  This  will  give  an 
emulsion  of  oxide  of  silver.  Now  wash  it,  treating 
it  as  a washed  emulsion,  and  add  a drachm  of  it  to 
an  ounce  of  a washed  emulsion  which  works  perfectly 
free  from  fog ; coat  a plate,  and  develop  it.  It  will  be 
found  that  inevitable  fog  is  produced.  In  this  case  the 
silver  oxide  (presumably  partially  reduced  to  the  metallic 
state,  since  the  oxide  is  an  unstable  compound)  acts  as 


PRELIMINARY  CONSIDERATIONS. 


9 


the  nucleus  on  which  the  silver  bromide  is  reduced  to  the 
metallic  state  by  the  alkaline  developer. 

It  must  be  borne  in  mind  that  the  invisible  image  must 
necessarily  be  composed  of  very  minute  particles  of  the 
altered  silver  salt.  If,  then,  such  a small  number  of  such 
particles  distributed  over  a film  are  sufficiently  powerful 
to  form  nuclei  for  the  development  of  the  image,  the  same 
minute  quantity  of  oxide,  or  chemically  produced  sub- 
haloid of  silver,  might  be  capable  of  producing  the  same 
results.  The  above,  then,  seems  to  be  the  explanation 
of  fog  in  emulsion  plates.  Now  as  to  the  remedies. 

It  is  well  known  that  when  we  have  an  excess  of 
soluble  haloid,  freedom  from  fog  is  secured.  In  some 
experiments  we  carried  out,  we  found  that  silver 
bromide  is  formed  before  any  other  silver  compound, 
except  the  iodide,  when  the  sensitive  salt  is  formed  from 
haloid  salts,  and  not  from  the  halogens  themselves.  Thus, 
if  potassium  bromide  be  contaminated  with  potash,  we 
shall  have  both  silver  bromide  and  silver  oxide  formed,  if 
an  excess  of  silver  nitrate  be  added ; but  if  there  be  a 
defect  of  the  nitrate  there  will  not  be  a trace  of  silver 
oxide,  but  only  silver  bromide.  Again,  if  we  take  bromide 
of  copper,  which  is  usually  contaminated  with  the  sub- 
bromide, as  already  stated,  it  will  be  found  that  the  bro- 
mide is  all  utilized  before  the  sub-bromide  is  attacked  at 
all ; and  if,  in  addition  to  the  bromide,  we  have  a metallic 
chloride  present,  which  may  be  contaminated  with  sub- 
chloride, the  order  in  which  they  will  combine  with  the 
silver  nitrate  is  : bromide,  chloride,  sub-bromide,  sub- 
chloride. Thus,  if  there  be  only  sufficient  silver  nitrate 
added  to  an  emulsion  to  combine  with  the  two  first  on 
the  list,  the  other  two  will  be  left  in  the  emulsion  as  harm- 
less compounds.  The  method  of  eliminating  fog  from 
the  finished  emulsion  in  which  there  is  at  first  an  excess 
of  silver  nitrate  is  thus  easy  to  guess,  and  we  have  the 
theoretical  explanation  of  Major  ftusselFs  statement  that 
a little  soluble  bromide  must  be  left  in  the  film  when 


10 


PRELIMINARY  CONSIDERATIONS. 


silver  bromide  is  formed  by  the  bath  in  the  usual  way.  It 
may  be  remarked,  parenthetically,  that  whether  the  image 
be  developed  by  the  alkaline  or  acid  method,  the  same 
result  must  hold  good.  Supposing  we  have  a washed 
emulsion  which  contains  bromide,  sub-bromide,  and  oxide 
of  silver,  and  also  a very  slight  excess  of  silver  nitrate. 
The  addition  of  certain  metallic  chlorides  or  of  hydro- 
chloric acid  will  at  once  convert  the  sub-bromide  and  oxide 
into  the  chloride  of  silver,  leaving  harmless  compounds 
behind.  The  metallic  chlorides  which  are  of  use  are  those 
which  readily  part  with  chlorine,  and  which,  therefore,  pre- 
ferably form  more  than  one  chloride,  such  as  gold,  copper, 
cobalt,  platinum,  &c.  When  other  chlorides,  such  as  of 
the  alkalies,  are  employed,  the  needful  substitution  may  not 
take  place,  because  the  affinity  of  the  alkali  for  the  chlor- 
ine is  greater  than  for  the  sub-bromide  ; and  therefore  the 
elimination  of  the  sub-bromide  is  not  effected.  Thus,  if 
all  the  silver  nitrate  in  original  excess  be  converted  into 
silver  chloride,  we  have  the  silver  sub-bromide  to  get  rid 
of.  Now,  supposing  we  are  using  sodium  chloride  as  a 
corrective,  then  we  should  have 

Silver  Sub-bromide  and  Sodium  Chloride , 

Ag2Br  + NaCl, 

which  can  form  no  new  saturated  silver  compound,  since 
an  atom  of  metallic  silver,  sodium,  bromide,  or  chlorine 
cannot  be  left  in  a free  state ; but  if  we  use  (say)  cobalt 
chloride,  we  have — 

Silver  Sub-bromide  and  Cobaltic  Chloride. 

AgsBr  + C0CI2 

which  can  form — 

Silver  Bromide  and  Silver  Chloride  and  Cobaltous  Chloride 
AgBr  + AgCl  + CoCl. 

The  CoCl,  or  sub-chloride  of  cobalt,  is  harmless,  and  can 
be  washed  out  of  the  film. 

It  will,  therefore,  be  seen  how  it  is  that  addition  of  these 
chlorides  to  a washed  emulsion  will  give  freedom  from  fog. 

Secondly,  if  an  excess  of  silver  nitrate  be  used,  it  is 


PRELIMINARY  CONSIDERATIONS. 


11 


evident  that  something  else  besides  a mere  chloride  will  be 
required,  since  the  sub-salts  and  oxides  would  be  formed. 
This  we  find  in  the  employment  of  an  acid,  or  of  a halogen 
itself,  or  both  together,  added  to  the  emulsion,  to  be  most 
rapidly  effective.  Whatever  is  used  is  best  added  to  the 
soluble  salts  before  the  silver  nitrate  is  added. 

Suppose  nitric  acid  alone  be  employed,  then  any  oxide 
or  carbonate  will  immediately  be  attacked,  as  also  any  of 
the  sub-bromides — such  as  of  copper.  Again,  if  aqua- 
regia  be  employed,  we  know  that  chlorine  is  evolved 
in  an  extremely  nascent  state,  and  that  this  would 
attack  either  oxide  or  sub-bromide,  fully  saturating  the 
unsatisfied  atom  in  the  latter.  If,  now,  silver  nitrate  be 
added,  silver  bromide  and  chloride  would  result  with  some 
compounds  (perhaps  such  as  the  chlorate),  which  would 
be  as  inert  as  producers  of  fog  as  the  silver  nitrate  itself. 

If  a halogen  be  employed  without  any  acid,  the  same 
result  would  occur.  Thus,  suppose  we  had  as  impurities 
an  oxide  and  a sub-bromide,  and  that  we  added  a solution 
of  bromine  to  it,  we  should  get  the  oxide  changed  to  a 
bromide  and  bromate  (the  latter  salt  of  which  is  experi- 
mentally proved  to  be  inert),  and  sub-bromide  changed  to 
a bromide. 

If  the  halogen  be  added  last,  when  there  is  an  excess  of 
silver,  it  is  probable  that  until  all  the  latter  is  converted  it 
will  exert  no  unfogging  action ; but  if  an  acid,  such  as 
nitric  acid,  be  added,  it  will  exert  its  proper  influence, 
though  slowly  ; for  it  will  convert  any  oxide  or  compounds 
of  the  oxide  into  nitrate,  and  from  the  silver  sub-bromide 
dissolve  away  the  loose  atom  of  silver,  converting  the  sub- 
bromide into  bromide  and  nitrate.  Thus — 


Silver  and  Nitric  mVP  Silver 

Sub-bromide  ana  Acids  give  Bromide 
4Ag  Br  + 6HNO3  = 4AgBr 


and 


and 


Nitrate  Oxide 

+ 4AgN03  + N0O3  + 


Water 

3H30. 


Or,  at  all  events,  a fresh  combination  will  be  made,  which 
is  unacted  upon  by  the  developer. 

There  is  also  a method  of  eliminating  fog  from  collo- 


12 


PRELIMINARY  CONSIDERATIONS. 


dion  dry  plates  when  coated,  without  doctoring  the  emul- 
sion at  aU.  This  need  not  apply  only  to  washed  emul- 
sions, but  it  can  be  effected  during  the  washing  of  the  plates 
prepared  by  the  unwashed  emulsion.  In  addition  to  the 
elimination  by  the  acids,  and  by  the  metals  forming  two 
bromides  or  chlorides,  we  can  further  effect  it  by  using  a 
solution  of  potassium  bichromate,*  permanganate  of  potash, 
or  peroxide  of  hydrogen,  and  other  oxidizing  agents,  such 
as  ferric-sulphate  and  ferric-oxalate.  The  reason  of  this 
seems  to  be  due  to  oxidation,  or  to  the  direct  formation  of  a 
new  product ; the  writer  is  still  engaged  in  experiments  on 
the  subject.  It  may  be,  in  the  first  case,  that  a minute 
quantity  of  silver  bichromate  is  formed  by  the  oxide,  or  that 
the  free  silver  atom  of  the  sub-bromide  is  oxidized,  and  then 
formed  into  silver  bichromate  ; with  the  second,  it  may  be 
that  the  manganese  salt  is  substituted  for  the  silver  salt,  and 
is  inert ; and  in  the  next  two  cases  it  may  be  that  the  silver 
salt  is  per-oxidized,  and  forms  an  oxy-bromide,  which  is 
unaffected  by  the  developer.  This  seems  probable,  since 
ozone  has  the  same  effect  on  the  fog. 

It  may  not  be  uninteresting  to  note  an  experiment  which 
throws  some  light  upon  this  point,  though  it  is  not  conclu- 
sive. If  a plate  be  coated  with  collodion  emulsion,  and  be 
allowed  to  thoroughly  darken  in  the  daylight,  and  then 
drops  of  the  above  oxidizing  agents  be  placed  on  different 
parts  of  the  film,  and  allowed  to  act  for  a few  minutes,  it 
will  be  found,  after  washing,  that  on  these  spots  the  colour 
and  appearance  of  the  film  will  remain  unaltered.  (Where 
the  manganese  has  been,  the  film  is  slightly  brown.)  Now, 
if  the  film  be  treated  with  sodium  hyposulphite,  the  parts 
where  all  have  been  will  become  transparent,  showing  that 
everything  except  the  collodion  has  been  dissolved  away, 
whilst  on  the  rest  of  the  plate  there  will  remain  a delicate 
layer  of  metallic  silver.  This  shows  that  the  loose  atom 
of  metallic  silver  attached  to  the  sub-bromide  has 


* This  can  he  used  with  gelatine  emulsions. 


PRELIMINARY  CONSIDERATIONS. 


13 


been  converted  into  a salt  soluble  in  hyposulphite  of 
sodium. 

Be  the  theory  what  it  may,  the  treatment  holds  good. 
Perhaps  with  collodion  plates  the  application  of  nitric 
acid  is  the  safest,  where  possible,  but  to  that  we  shall  refer 
later  on. 

Dr.  Eder  has  also  shown  that  potassium  ferri-cyanide 
and  potassium  bromide  will  cause  the  same  result.  The 
ferri-cyanide  acts  as  follows  : — 


Silver 

Sub-bromide 

4AgoBr 


and 

+ 


Ferri-cyanide 
of  Potassium 


2K6Fe3Cyi2 


give 


Ferrocyanide  ■,  Ferrocyanide  ■,  Silver 
of  Potassium  ana  of  Silver  ana  Bromide. 

3K4FeCy6  + Ag4FeCy6  + 4AgBr 


The  potassium  bromide  converts  the  ferro-cyanide  of 
silver  into  bromide,  and  ferro-cyanide  of  potassium  is 
formed.  Thus — 


Ferrocyanide 
ot  Silver 


Ag4FeCy6 


and 

+ 


Potassium 

Bromide 

KBr 


give 


Ferrocyanide  of 
Potassium 

K4FeCy6 


, Silver 
aEa  Bromide 

+ AgBr 


From  the  foregoing  it  will  be  seen  that  fog  may  be 
produced  by  inorganic  matter  present  with  the  silver  salt ; 
and  further  on  it  will  be  seen  that  it  may  be  produced 
during  development  and  in  emulsification.  Regarding 
this  last  point  there  is  more  to  be  said  in  regard  to  gelatine 
emulsion,  and  which  will  be  found  more  fully  treated  of 
later  on.  Suffice  it  to  say  that  gelatine  itself,  when  decom- 
posed to  any  extent,  has  an  alkaline  reaction,  ammonia 
being  one  of  the  products,  and  that  this  will  reduce  the 
silver  bromide  held  in  suspension  in  it,  unless  means  be 
taken  to  overcome  the  effect  of  the  alkalinity,  or  to  neutra- 
lize the  alkalinity.  In  other  words,  decomposing  gelatine 
is  a feeble  developer  (or  reducer  of  the  silver  salt),  and 
may  cause  fog.  The  fog  caused  by  the  reduction  of  the 
bromide  to  the  metallic  state  is  much  more  difficult  to  treat 
than  any  other,  for  the  mere  conversion  of  the  metallic 
silver  into  oxide  is  useless  (see  page  8).  More  vigorous 
treatment  is  required.  This  shows  that  a collodion  emul- 
sion is  much  more  readily  unfogged  than  a gelatine  one, 


14 


PRELIMINARY  CONSIDERATIONS. 


since  in  the  former  the  reduction  of  the  silver  salt  to  the 
metallic  state  rarely,  if  ever,  occurs.  With  collodion  the 
danger  is  minimized,  and  acidity  rather  than  alkalinity  is 
to  he  apprehended.  $ 

With  gelatine  plates  it  is  inadmissible  to  use  any 
substance  which  may  attack  the  gelatine ; thus  the  appli- 
cation of  acids  is  not  to  be  thought  of,  nor  hydroxyl,  nor 
permanganate  of  potash.  Chloride  of  copper  may  be 
employed,  but  the  safest  plan  is  to  use  either  bichromate 
of  potash  or  the  ferricyanide  of  potassium  with  the 
bromide  of  potassium ; but  to  this  we  shall  refer  at  greater 
length  in  the  practical  part  of  the  work. 


CHAPTEK  II. 


ALKALINE  DEVELOPMENT. 

It  will  be  noticed  that  all  emulsion  plates  are  developed 
either  by  alkaline  development,  or  by  ferrous  oxalate 
development,  and  we  propose  to  consider  these  two  deve- 
lopers from  their  theoretical  point  of  view.  It  may  be  said, 
first  of  all,  that  iodide  is  not  amenable  to  alkaline  deve- 
lopment, except]  under  conditions  which  render  it  use- 
less to  attempt  ; the|  bromide  and  chloride  are  amenable 
to  it. 

An  alkaline  developer  consists  of  a strong  absorbent  of 
oxygen,  an  alkali,  and  a soluble  bromide  or  chloride.  The 
two  first  are  the  only  two  which  are  essential  for  the  re- 
duction of  a salt  of  silver  to  the  metallic  state.  Thus,  if 
we  take  precipitated  bromide  of  silver*  and  add  to  it  a 
solution  of  pyrogallic  acid  and  ammonia,  we  shall  find 
that  it  is  rapidly  reduced  to  the  metallic  state.  If,  how- 
ever, we  precipitate  the  silver  bromide  in  the  dark,  and 
add  to  the  developing  solutions  a little  bromide  of  potas- 
sium, we  find  that  the  mass  is  reduced  more  slowly,  the 


* Precipitated  by  dissolving  a little  bromide  of  potassium  in  water,  and 
adding  to  it  silver  nitrate,  and  then  washing. 


16 


ALKALINE  DEVELOPMENT. 


soluble  bromide  acting  as  a retarder  to  the  reduction.  If 
we  have  a film  which  has  been  exposed  to  a camera  image, 
and  develop  by  the  unretarded  solution,  we  shall  find  a re- 
duction all  over  the  surface  ; whereas  if  we  use  one  with 
the  retarder  in,  we  shall  find  that  with  it  the  image  deve- 
lops properly  ; in  other  words,  the  alkaline  developer  has  a 
tendency  to  act  on  the  sub-bromide  more  than  on  the  silver 
bromide  which  has  been  unacted  upon  by  light.  During 
the  operation  of  the  reduction  of  the  silver  bromide  or  sub- 
bromide to  the  metallic  state  we  have  an  alteration  in  the 
developing  solution,  the  pyrogallic  acid  becomes  oxidized, 
and  part  of  the  alkali  enters  into  combination  with  the 
eliminated  bromine. 

The  following  equation  gives  an  idea  of  what  will  take 
place,  though  it  is  not  strictly  accurate  in  a chemical 
point  of  view. 


Silver  Sub-Bromide  Pyrogallic  Acid  and  Ammonia  give 

2Ag.>Br  -f-  Pyrogallic  Acid  -f-  2NH4HO 

Silver  Oxidized  Pyrogallic  Acid  Ammonium  Bromide  and  Water 
4Ag  -f  Pyro.  0 -f  2NH4Br  -f  H20 

The  whole  of  the  action  depends  upon  the  affinity  for 
oxygen  of  the  oxygen  absorbent.  The  stronger  its  affinity 
for  oxygen,  the  greater  the  energy  of  development.  The 
energy  of  this  affinity  is  checked  by  a soluble  bromide ; 
why  this  is,  is  a moot  point  at  present,  and  deserves 
rigorous  investigation.  It  is  quite  certain,  however, 
that  by  checking  its  affinity,  not  only  is  it  less  liable  to 
reduce  the  unaltered  bromide,  but  that  it  also  reduces 
more  tardily  the  sub-bromide.  An  absorbent  of  oxygen, 
which  is  capable  of  reducing  the  sub-bromide  alone  at  the 
first  shock  without  reducing  the  bromide,  must  be  a better 
agent  to  use  than  pyrogallic  acid,  which  requires  such  a 
retarder.  Such  an  oxygen  absorbent  has  been  found  by 
the  writer  in  hydrokinone,  which,  under  ordinary  circum- 
stances, has  no  tendency  to  reduce  the  silver  bromide,  and 
it  has  a greater  affinity  for  oxygen  than  any  known  organic 


ALKALINE  DEVELOPMENT. 


17 


substance.  Unfortunately,  its  value  is,  as  a developer, 
diminished,  owing  to  its  high  price. 

An  alkaline  developer  is-  one,  then,  which  reduces  the 
silver  sub-bromide  to  the  metallic  state,  and  leaves  the 
silver  bromide  intact.  F rom  what  we  have  said  it  is  evi- 
dent that  silver  sub-bromide  on  an  exposed  plate  must  ex- 
ist in  the  minutest  quantity — in  fact,  be  indistinguishable 
by  ordinary  chemical  analysis.  How  comes  it,  then,  that  a 
visible  image  can  be  developed  at  all,  since  the  reduced 
silver  would  be  even  more  invisible  than  the  sub- bromide  ? 
Experiment  teaches  us  that  the  bromide  of  silver  cannot 
exist  in  close  contact  with  freshly-formed  metallic  silver. 
Hence  immediately  metallic  silver  is  formed  by  the  deve- 
loper, the  molecules  of  sub-bromide  in  contact  with  it 
become  sub-bromide.  Thus 

Silver  and  Silver  Bromide  make  Silver  Sub-Bromide. 

Ag  + AgBr  = AgjBr 

The  freshly-formed  sub-bromide  is  in  its  turn  attacked, 
and  reduced  by  the  developer  to  the  metallic  state,  and 
thus  the  image  is  gradually  built  up  in  metallic  silver. 

From  chemical  analogy  it  may  be  assumed  that  the  at- 
tractive force  of  the  particles  altered  by  light  is  most 
vigorous  when  freshly  formed,  and  that  metallic  silver 
also  has  the  same  energy  of  attraction  when  it  is  freshly 
deposited,  though  it  seems  probable  that  in  development 
there  is  a state  in  which  the  sensitive  salt  can  be  placed 
in  which  it  loses  its  power  of  attraction  in  a great 
measure.  With  the  weak  alkaline  developer  the  silver 
is  reduced  but  slowly  from  the  bromide,  and  hence  it 
becomes  less  u nascent,”  if  we  may  use  the  term,  than  it 
is  when  it  is  rapidly  reduced,  and  when  the  next  particle 
to  it  is  also  rapidly  reduced  and  ready  to  bind  itself  to  the 
silver  just  deposited.  Slow  deposition  of  silver  is  also 
not  conducive  to  density  (as  we  know  by  experience 
when  silvering  mirrors),  and  this  alone  points  to  the  ad- 
vantage of  an  energetic  developer.  Again,  from  chemical 


18 


FERROUS-OXALATE  DEVELOPMENT. 


analysis  of  the  developer  alter  it  has  been  used,  it  is  found 
that  a weakly  alkaline  solution  is  only  capable  of  reducing 
a small  amount  of  the  bromide  compared  with  a concen- 
trated solution. 

It  will  be  noticed  that  the  alkaline  developer  is  nothing 
more  nor  less  than  a silvering  solution  minus  the  silver,  as 
used  for  silvering  mirrors,  the  pyrogallic  acid  taking  the 
place  of  grape  sugar  or  sugar  of  milk.  The  reduction  of 
the  bromide  toNthe  metallic  state  is  effected  in  the  same 
way  that  the  reduction  of  the  ammoniacal  solution  of 
silver  is  effected. 

It  will  be  observed,  that  various  formuhe  are  given  for 
alkaline  development ; in  one  ferro-cyanide  of  potassium 
plays  a part,  and  in  another  sulphite  of  soda.  The  value 
of  both  these  appears  to  be  that  they  oxidize  with  the 
pyrogallic  acid  ; whether  in  the  absolute  act  of  develop- 
ment, or  merely  by  absorption  of  oxygen  from  the  air,  is 
undecided.  In  any  case,  the  longer  the  pyrogallic  acid 
remains  unoxidized,  the  more  effectual  should  be  the 
development. 

The  hydrosulphite  developer  may  be  classed  amongst 
the  alkaline  developers. 

We  next  have  to  consider  the  ferrous  oxalate  developer, 
and  it  matters  but  little,  as  regards  theoretical  considera- 
tions, as  to  which  way  it  is  formed.  It  will  be  seen  by 
the  formula  given  later  that  the  ferrous  oxalate  developer 
is  in  reality  a solution  of  ferrous  oxalate,  in  neutral 
potassium  oxalate.  The  latter  salt  exercises  no  develop- 
ing  action,  but  is  rather  a retarder  to  development  than 
otherwise.  We  have  therefore  only  to  consider  the  action 
of  ferrous  oxalate  on  silver  sub-bromide,  and  it  may  be 
expressed  as  follows  : — 

Ferrous  Oxalate  and  Silver  Sub-Bromide  give 

3(Fe,C204)  + 2Ag-.Br  = 

Ferric  Oxalate  and  Ferrous  Bromide  and  Silver 

Fe2,(C204)3  + FeBr2  + 4Ag 

By  which  it  will  be  seen  that  a metallic  bromide  is 
formed,  together  with  ferric  oxalate. 


FERROUS-OXALATE  DEVELOPMENT. 


19 


Now,  as  has  already  been  pointed  out,  ferric  oxalate 
destroys  the  developable  image  (see  page  12),  hence  it  is 
a retarder.  Ferrous  bromide  is  also  a greater  retarder  of 
development  than  the  potassium  bromide.  Experience 
has  shown  the  writer  that  the  addition  of  a small  quantity 
of  hyposulphite  makes  development  much  more  rapid,  and 
that  a gelatine  plate  requires  less  exposure  with  it.  Let 
us  trace  what  happens  first  as  regards  the  ferrous  bromide 
formed : — 

Sodium  Hyposulphite  and  Ferrous  Bromide  give 

Na2S2(>3  + FeBr2  = 

Hyposulphite  of  Iron  . and  Sodium  Bromide 
Fe,S203  -}-  2NaBr2 

Whence  it  will  be  seen  that  the  extra  retarding  influence 
of  the  ferrous  bromide  vanishes,  and  the  milder  retarding 
sodium  bromide  is  formed.  Again,  if  we  trace  what  will 
happen  when  sodium  hyposulphite  is  added  to  ferric 
oxalate,  we  shall  find  that  ferrous  hyposulphite  and  oxa- 
late are  formed,  and  also  a sodium  oxalate.  Dr.  Vogel 
believes  that  the  good  effect  of  the  hyposulphite  is  due  to 
the  hyposulphite  of  iron  formed.  We  ourselves,  at  the 
present  moment,  are  not  inclined  to  hold  to  this  explana- 
tion. It  seems  almost  more  likely  that  the  destruction  of 
the  ferric  salt  immediately  on  its  formation  is  one  cause 
of  the  acceleration. 


CHAPTER  III. 


DARK  ROOM  AND  ITS  FITTINGS. 

We  have  thought  it  may  be  advantageous  to  give  a slight 
outline  on  the  requirements  of  the  dark  room  and  its 
fittings.  The  size  of  the  dark  room  may,  of  course,  vary, 
but  it  may  be  remarked  that  a place  six  feet  square  is  a 
space  large  enough  in  which  to  work  comfortably,  but 
then  the  arrangement  of  the  room  must  be  adapted  to  it. 
A sample  of  an  arrangement  is  given  in  the  figure. 


0 I 2 3 4-56  FJEET- 

1  * 1 1 * r“l 


C C 

' 

A 

B 

A 

D 

f 

Fig.  2. 

E is  the  sink  ; A A are  two  working  tables.  On  the  left, 
over  A,  may  be  placed  a glass  shelf,  running  along  the 


DARK  ROOM  AND  ITS  FITTINGS. 


21 


left  wall  towards  the  drying  cupboard,  D.  The  right- 
hand  table,  A,  may  be  used  for  the  developing  bottles 
and  apparatus.  The  door  of  the  dark  room  should  open 
outwards,  if  possible,  and  be  covered  by  a curtain, 
which  depends  on  to  the  ground,  thus  shutting  out  all 
light  which  would  otherwise  get  through  the  chink 
between  the  door  and  the  floor.  Too  many  precautions 
to  exclude  white  light  cannot  be  taken,  since  gelatino- 
bromide,  if  it  is  to  take  the  place  of  collodion,  should  be 
extremely  sensitive  to  it,  however  feeble  it  may  be. 

Water  A rrangements. — It  is  always  useful  to  have  water 
laid  on  to  a dark  room,  but  in  many  cases  it  is  impossible  ; 
in  that  case  we  recommend  that  a two-gallon  jar  be  placed 
some  three  feet  about  A (fig.)  on  the  right  hand,  a hole 
being  bored  about  two  inches  from  the  bottom.  A cork 
with  a pierced  hole,  in  which  is  passed  a small  piece  of 
glass  tubing,  should  fill  up  this  orifice,  and  on  the  glass 
tube  should  be  drawn  a piece  of  black  india-rubber  tubing 
of  a convenient  length,  to  which  an  American  clip  should 
be  attached.  If  a hole  be  bored  slantingly  through  the 
clip  so  that  the  india-rubber  tube,  when  passed  through  it, 
comes  to  the  termination  of  the  jaws  of  the  clip,  this 
arrangement,  which  was  first  described  to  us  by  Mr. 
England,  will  answer  better  than  more  elaborate  con- 
trivances. When  water  is  laid  on  from  the  main,  a rose 
is  a very  desirable  adjunct  to  the  tap,  since  it  gives  a jet 
which  has  no  force,  and  which  is  like  a shower  or  spray. 

Drying- Cupboards. — The  principles  on  which  a drying- 
box  should  be  made  should  be  apparent,  though  in  many 
forms  they  are  neglected.  The  first  principle  which 
should  be  carried  out  is  that  the  air  passing  through  it 
should  be  capable  of  taking  up  moisture.  It  very 
often  happens  that  the  air  which,  in  some  contrivances, 
is  passed  through  the  drying-box  is  nearly  saturated 
with  moisture,  hence  it  can  take  up  but  very  little  more, 
and  plates  dry  slowly.  How,  then,  can  it  be  made 
to  absorb  more?  It  may  be  done  by  causing  it  to 


22 


DARK  ROOM  AND  ITS  FITTINGS. 


bubble  through  sulphuric  acid,  or  by  passing  it  through 
dry  chloride  of  calcium ; but  in  order  for  this  to  be  effective, 
the  drying-box  must  not  only  be  light-tight,  but  also  air- 
tight, since  the  air  would  find  its  way  immediately 
through  any  small  chink  or  cranny  sooner  than  force  its 
way  through  these  obstructions.  A better  mode  is  to 
warm  the  air,  since  it  is  well  known  that  warm  air  |will 
take  up  more  moisture  than  cooler  air,  and  it  is  on  J this 
principle  that  some  efficient  drying-boxes  are  constructed. 

A good  type,  and  an  excellent  one,  too,  is  that  shown|in 
fig.  3.  It  is  Mr.  England’s  plan,  and  if  constructed  as  in 
the  sketch  would  take  any  plates  up  to  12  by  12. 


A box  is  made  of  the  dimensions  given,  and  one  side 


DARK  ROOM  AND  ITS  FITTINGS. 


23 


is  hinged,  and  opens  as  shown.  This  side  has  a fillet 
placed  round  it,  so  that  on  shutting  up  no  light  can 
enter  the  interior  of  the  box.  Through  the  centre  of  the 
box  runs  a gas  pipe,  at  the  bottom  of  which  is  inserted  a 
small  tube  closed  at  the  end,  and  on  the  side  of  which  is 
pierced  a small  hole.  To  this  hole  gas  is  led,  and  a very 
small  jet  is  lighted  in  the  gas  pipe.  At  the  bottom  of  the 
box,  and  at  the  top,  are  two  holes  of  about  three  to  four 
inches  diameter,  and  above  two  tin  tubes,  some  twelve 
inches  long,  are  fitted  into  these  tubes  as  shown  in  the 
diagram.  It  will  be  noticed  that  the  gas  piping  passes 
through  the  centre  of  these  two  tubes.  Round  the  gas 
pipes  are  fitted  two  discs  of  blackened  card  or  tin,  one  of 
which  is  placed  two  inches  above  the  bottom  hole,  and  the 
other  the  same  distance  from  the  top  hole.  These  pre- 
vent light  striking  down  the  tin  tube  into  the  box.  The 
plates,  when  set,  are  laid  on  pairs  of  wires  stretched  across 
the  box,  as  shown  in  the  diagram,  and  a box  of  the  above 
dimensions  may  take  from  half  to  one  dozen  plates  on  each 
side  of  the  central  pipe. 

Plates  dried  in  such  a drying-box  are  ready  for  use  four 
or  five  hours  after  coating.  A small  thermometer  should 
be  hung  on  the  cupboard  door,  to  enable  the  temperature 
to  be  noted. 

The  rationale  of  this  fairly  rapid  drying  is  that  the  gas 
piping  gets  heated,  warms  the  air  in  contact  with  it,  which 
ascends  through  the  top  tin  tube,  and  a current  of  fresh 
air  comes  up  through  the  bottom  one.  A constant  change 
of  air,  more  than  a very  dry  or  hot  air,  is  the  object  to 
be  attained. 

We  are  in  duty  bound  not  only  to  give  its  excellencies, 
but  also  to  point  out  any  defects.  In  hot  weather  we  have 
found  that  plates  dried  very  close  to  the  central  pipe  are 
apt  to  run ; the  heat  is  communicated  to  the  iron  wires,  and 
the  glass  takes  it  up,  and  the  gelatine  is  apt  to  melt  when 
the  plate  touches  the  wires.  This  is  evidently  due  to 
conduction,  and  we  believe  that  it  is  better  to  have  a non- 


24 


DAEK  ROOM  AND  ITS  FITTINGS. 


conducting  medium  in  contact  with  the  glass.  Small  loose 
cylinders,  about  half-an-inch  long,  of  pipe-clay,  can  he 
readily  baked  and  slipped  over  the  iron  bars,  and  each  end 
of  the  plate  supported  by  them.  For  summer  weather, 
when  the  air  is,  as  a rule,  dry,  it  is  a good  plan  to  have  a 
small  gas  jet  placed  just  above  the  box  in  the  iron  gas 
tube.  This  heats  the  air  in  the  zinc  tube,  and  a draught  is 
created  through  the  box;  by  this  means  the  air  is  not 
above  the  summer  temperature,  and  is  not  so  quick-drying. 

The  plan  recommended  by  Dr.  Van  Monckhoven  is  one 
which  has  long  been  in  use  in  England,  but  he  has  des- 
cribed it  as|follows  : — im  The  drying-box  (fig.  4)  is  easily 


Fig.  4. 

made,  and  consists  of  a box  of  thick  wood,  on  the  top  of 
which  is  a zinc  pipe  to  connect  it  with  a chimney.  At 
the  bottom  is  another  pipe,  but  with  an  elbow  to  prevent 
light  from  entering.  Horizontal  shelves  are  placed  in  the 
interior,  so  that  the  current  of  air  obtained  by  the  draught 
in  the  chimney  goes  over  each,  one  after  the  other.  This 


DARK  ROOM  AND  ITS  FITTINGS. 


25 


box  ought|to  be  placed  in  a warm  and  very  dark  room. 
As  to  thefnecessity  ot  warmth  in  the  room,  we  demur. 
It  is  not  necessary  if  arrangements  be  made  for  burning 
a gas  jet  in  the  top  tube,  so  as  to  create  a draught. 

Mr.  A.  Cowan  has  also  described  in  the  Photographic 
Almanac  a drying  box  for  dry  plates  which  is  essentially 
correct  in  principle,  and  no  doubt  answers  well.  He  says  : 
u It  often  happens  in  very  damp  weather  that  gelatine 
negatives  refuse  to  dry  for  hours,  and  even  when  flooded 
with  spirit  take  a considerable  time. 

u To  those  who  do  not  possess  a good  drying  cupboard 
the  following  is  offered  as  a thoroughly  efficient  substitute, 
which  anyone  can  make  for  himself  with  a little  help  from 
the  blacksmith. 

u The  annexed  diagram  will  explain  itself.  The  box 


may  be  of  any  form  most  convenient,  but  the  more  shallow 
the  better.  . The  one  in  actual  use  stands  on  an  ordinary 
work-bench,  and  the  gas-burner,  and  iron  cone,  &c.,  on 


26  DARK  ROOM  AND  ITS  FITTINGS. 

the  floor,  enclosed  with  a few  bricks  piled  up  to  keep  in 
the  heat  and  protect  any  woodwork.  A very  good  pro- 
portion for  the  cupboard  is  thirty  inches  high,  thirty  inches 
wide,  and  ten  inches  deep  from  back  to  front.  The  front 
is  closed  up  at  the  lower  part  about  six  inches,  and  a 
sliding  door  running  in  grooves  closes  the  upper  part  all 
but  about  half  an  inch  at  the  top,  a balance  weight  over 
a pulley  supporting  it  in  any  position  required.  This  is 
found  a much  better  way  than  having  doors  opening  on 
hinges,  for  various  reasons. 

u The  current  of  warm  air  is  conveyed  in  at  the  bottom 
through  a three-inch  circular  opening,  the  iron  stove-pipe 
arrangement  being  screwed  on  underneath.  Above  the 
opening,  at  a little  distance,  is  supported  a thin  shelf  of 
wood  about  an  inch  smaller  all  round  than  the  inside  of  the 
box,  which  acts  as  a diffuser,  and  stops  the  current  of  hot 
air  from  rushing  up  in  one  spot.  Above  this,  at  any  con- 
venient height,  two  bars  are  fixed  to  carry  the  feet  of 
the  drying  rack  containing  the  plates.  It  will  be  found 
that  plates  will  dry  without  running  at  a very  considerably 
higher  temperature  than  that  at  which  gelatine  melts  if 
the  heated  air  be  kept  in  continual  motion.” 


CHAPTER  IV. 


ILLUMINATION  OF  THE  DARK  ROOM. 

In  all  emulsion  processes,  whether  collodion  or  gelatine, 
great  precautions  have  to  he  taken  as  to  the  light 
in  which  the  plates  are  prepared,  since  they  are  neces- 
sarily exposed  to  its  action  for  some  considerable  time. 
There  are  many  persons  who  attempt  to  prepare  emul- 
sions who  fail,  and  the  failure  may  often  be  traced  to  the 
improper  lighting  of  the  dark  room.  F or  development,  a 
light  which  would  slightly  fog  a plate  during  pre- 
paration may  be  used,  since  it  is  not  necessary  that  it 
should  be  exposed  to  its  action  more  than  a second  or  two, 
which  would  not  be  sufficient  exposure  to  cause  any  per- 
ceptible fog.  When  once  development  begins,  the  ingress 
of  more  actinic  light  has  but  little  eifect,  since  there  is 
sufficient  bromide  used  in  the  development,  with  the 
alkaline  development,  to  render  the  silver  salt  insensitive  ; 
or,  if  ferrous  oxalate  be  employed,  the  solution  itself  is  of 
a colour  which  effectually  cuts  off  all  light  that  would 
rapidly  harm  the  image.  We  have  made  these  remarks, 
not  to  discourage  the  idea  that  a perfectly  safe  light 
should  be  used,  but  to  show  that  when  such  cannot 
be  procured,  as  on  tour,  it  is  possible  to  develop 
plates  without  any  danger.  It  is  necessary,  first  of 
all,  to  know  what  kind  of  plates  are  to  be  prepared, 


28 


ILLUMINATION  OF  THE  DARK  ROOM. 


and  worked,  before  deciding  what  light  to  admit  to  the 
dark  room.  For  instance,  with  collodio-bromide,  an 
orange  light  will  be  sufficient ; but  with  gelatine  plates 
containing  pure  bromide,  a ruby  light  in  which  there  is 
no  green  is  absolutely  essential.  It  is  safe,  however,  in 
all  cases,  to  have  a red  light,  and  we  recommend  it  for 
general  adoption,  since  every  kind  of  plate  can  be  worked 
in  it. 

One  maxim  to  remember  is,  that  if  the  quality  of  the 
light  be  correct,  the  quantity  may  be  unlimited.  To 
make  this  more  clear,  a diagram  from  another  work* 
is  reproduced,  from  which  a notion  can  be  obtained 
as  to  the  light  to  which  different  plates  are  sensi- 
tive, and  the  media  which  may  be  accepted  to  cut  off  that 
light. 

No.  1 may  be  omitted  from  consideration,  since  it  is 
sensitive  to  all  rays,  and  no  filtered  daylight  is  admissible 
where  it  is  employed ; but  Nos.  2,  3,  and  4 should  be 
studied.  When  a streak  of  white  light  is  passed  through 
a prism  it  is  spread  out  into  its  component  colours,  and 
in  14  they  are  represented  as  white.  The  black  portions 
in  2,  3,  and  4 of  the  diagram  show  the  rays  of  light  in 
every  case  which  do  not  affect  a sensitive  plate.  The 
white  and  half-tints  represent,  as  approximately  as  can 
be  shown  in  a wood-cut,  the  relative  sensitiveness  of 
the  plates  to  the  different  rays  forming  white  light; 
the  degree  of  sensitiveness  being  indicated  by  the 
degree  of  whiteness.  It  will  be  noticed  that  the 
gelatino-bromide  and  collodio-bromide  plates  are  sensi- 
tive to  the  confines  of  the  red,  and  some  specimens  of 
the  former  are  also  sensitive  well  into  the  red,  whilst  the 
bromo-iodide  is  only  sensitive  to  the  confines  of  the 
yellow.  Next  we  need  only  turn  our  attention  to  Nos.  5, 
6,  7,  8,  9,  10,  and  12.  In  these  are  shown  the  rays  of  light 
which  pass  through  different  coloured  glasses  and  dyes. 


* “ Instruction  in  Photography  ” (Piper  and  Carter),  4th  edition. 


ILLUMINATION  OF  THE  DARK  ROOM, 


29 


o 


1.  Special  collodio- bromide. 

2.  Gelatino-bromide. 

3.  Collodio-bromide. 

4.  Bromo-iodide. 

5.  Cobalt  glass. 

6.  Ruby  glass. 


7.  Chrysoidine. 

8.  Magenta. 

9.  Flashed  oiange. 

10.  Stained  red  glass. 

1 1 . Bottle-green  glass. 

12.  Aurine. 


13.  Quinine. 


30 


ILLUMINATION  OF  THE  HARK  ROOM. 


Ruby  glass  would  be  a perfect  protection  for  nearly  every 
plate  were  it  not  that  a certain  amount  of  blue  light 
passes  through  one  thickness  of  it.  When  two  thick- 
nesses are  used  the  blue  is  imperceptible.  By  the  use  of  a 
combination,  orange  glass  and  ruby,  or  stained  red  glass 
and  ruby,  the  light  allowed  to  pass  through  is  such  as  will 
not  affect  most  of  the  sensitive  plates,  since  the  orange 
or  stained  red  entirely  cuts  off  the  blue  which  may  per- 
meate the  ruby  glass.  Several  persons  with  whom  the 
writer  has  come  in  contact  have  told  him  that  they  pre- 
pare plates  so  sensitive  to  the  red  that  the  light  passing 
through  any  number  of  thicknesses  of  ruby  glass  proves  an 
ineffectual  protection  to  the  plates  they  prepare.  Unless 
ruby  glass  were  added  till  total  darkness  supervened,  there 
is  nothing  to  surprise  us  in  this  statement,  as  the  red  light 
which  filters  through  three  or  four  thicknesses  of  ruby  glass 
has  the  same  quality  as  that  which  filters  through  two 
thicknesses.  What  they  really  express  is  that  they  pre- 
pare plates  which  are  in  reality  sensitive  to  red  light. 
When  this  is  the  case,  the  development  and  preparation 
of  such  an  emulsion  become  a nuisance,  and  are  probably 
more  of  a scientific  than  of  a practical  value,  since  the 
same  sensitiveness  can  be  produced  without  any  liability 
to  veiling  of  the  image  through  the  impact  of  light  of  such 
low  refrangibility  on  the  plate.  For  an  ordinary  dark 
room  we  recommend  that,  if  a north  light  be  obtainable 
for  the  window,  one  thickness  of  ruby  and  one  of  stained 
red  or  orange  glass  be  employed.  As  to  dyes,  it  will  be 
seen  that  if  glass  be  coated  with  aurine  on  one  side,  and 
magenta  on  the  other,  the  same  spectral  quality  will  be 
obtained.  If  plates  very  sensitive  to  the  red  be  prepared, 
one  thickness  of  cobalt  glass  and  one  of  stained  red  will 
be  the  best  combination  to  use ; but,  as  we  said  before, 
plates  requiring  such  a light  by  which  to  develop  should 
not  find  a place  in  a photographer’s  hands.  If  the  sun 
shine  on  the  window  during  any  part  of  the  day,  it  is  well  to 
have  a screen,  which  can  be  placed  against  the  window- 


ILLUMINATION  OF  THE  DARK  ROOM.  31 

frame  (it  can  be  hinged  from  the  top,  and  pulled  up  as  a 
flap  by  a small  pulley  arrangement),  covered  with  orange- 
coloured  paper.  This  diffuses  the  light,  and  renders  any 
chemically  active  rays  which  can  possibly  filter  through 
it  less  hurtful.  It  is  not  always  practicable,  however,  to 
work  by  day,  and  then  it  becomes  necessary  to  resort  to 
artificial  light,  and  that  must  be  of  the  same  character  as 
the  filtered  daylight.  Now,  candle  and  gas  light  have 
not  the  same  amount  of  blue  in  them  as  the  light  from 
the  sun,  hence  the  screen  used  for  shielding  such  sources 
need  not  be  quite  so  perfect.  In  our  practice  we  have  a 
common  stable  lantern  fitted  up  for  this  purpose.  Holes 
are  pierced  at  the  bottom  of  it  for  the  indraught  of  air, 
and  holes  at  the  top  of  the  sides  for  the  outdraught. 
To  pi  event  any  light  striking  the  ceiling,  we  have  had  a 
tin  cover  fitting  round  the  lantern*  at  the  top,  and  sloping 
45°  downwards,  by  which  means  any  light  glancing 
through  the  holes  strikes  the  shade  and  is  reflected  down- 
wards. The  glass  walls  are  coated  with  magenta  and 
aurine  dissolved  in  common  shellac  varnish.  Thomas’ 
ruby  varnish  answers  well.  Its  colour  seems  to  be  due  to 
the  combination  of  the  ssme  two  dyes 

Some  dry  plate  men  we  know  have  gas  burning  close 
outside  a ruby  glazed  window  which  opens  into  an  ad- 
joining room,  but  it  is  not  every  one  who  can  have  such 
an  arrangement. 

For  developing  plates  away  from  home,  we  have  found 
that  a useful  piece  of  apparatus  can  be  easily  made. 
Take  a sheet  of  cardboard  of  the  size  of  about  2 feet  by 
1 foot  6 inches.  Lay  off  from  the  2 feet  side  distances  of 
fi  inches  from  each  corner,  and  with  a penknife  cut  half 
through  the  card  in  a line  parallel  to  the  ends.  These 
will  form  flaps,  which  can  be  folded  over  to  meet  in  the 
centre.  From  the  centre  portion,  and  6 inches  from  the 
bottom,  mark  out  a square  of  8 inches ; cut  round  three 


* Some  lanterns  are  made  with  this  arrangement. 


3 2 


ILLUMINATION  OF  THE  DARK  ROOM. 


of  tlie  sides,  but  only  half  cut  through  the  bottom  side, 
the  penknife  being  applied  from  the  inside  of  screen. 
This  will  allow  a square  flap  to  fold  downwards  towards 
the  outside.  On  the  inside  of  the  opening  may  be  pasted 
or  hung  two  of  orange  paper ; or  a sheet  of  paper  dyed 
deeply  with  a mixture  of  aurine  and  aniline  scarlet  may 
be  glued  to  it.  The  candle  is  placed  behind  the  screen, 
which  should  stand,  supported  by  the  two  wings,  in  front 
of  the  operator.  A piece  of  board,  or  a piece  of  tin,  may 
rest  on  the  screen,  and  thus  cut  off  diffused  light  from  the 
ceiling.  We  have  developed  many  plates  with  such  a 
light,  and  lost  none  by  veiling  of  the  image.  When 
packed  for  travelling  the  flaps  are  folded  up,  and  it  can 
be  placed  in  the  portmanteau. 

A useful  portable  lantern  is  made  from  a Chinese  lan- 
tern. We  first  saw  it  adapted  in  Mr.  Gabon’s  hand ; but 
Dr.  Hermann  F ol  has  given  a practical  method  of  its  con- 
struction in  the  Photographic  News.  He  describes  it 
as ] follows  : — u The  most  portable  lantern  I make  by 


painting  over  common  white  paper  Chinese  lanterns  with 
collodion  ^containing  castor  oil  and  fuchsine.  T he  top 


ILLUMINATION  OF  THE  DARK  ROOM. 


33 


and  bottom  of  the  lantern  are  made  each  of  two  thin 
metal  plates  fastened  together  by  three  small  chains. 
Each  plate  is  pieced  with  holes,  and  each  pair  is  fastened 
to  the  chains  so  that  the  holes  do  not  correspond,  and 
half-an-inch  remains  between  the  two  plates.  No  white 
light  can  then  find  its  way  out.  The  upper  pair  is,  of 
course,  unfixed,  and  may  be  lifted  out  to  get  access  to 
the  candle.  This  lantern  folds  up  into  the  smallest 
possible  compass,  and  when  in  use  perfectly  precludes  all 
actinic  light  without  getting  hot. 


D 


CHAPTER  V. 


COLLODION  EMULSIONS. 

The  first  emulsions  of  which  we  shall  treat  will  he  the 
collodion  emulsions,  for  which,  at  one  time  or  another,  a 
great  variety  of  formulas  have  been  published.  It  would 
be  impossible  to  give  all  which  have  from  time  to  time 
been  given  in  the  various  photographic  publications, 
but  a selection  has  been  made  of  what  the  writer  conceives 
to  be  the  most  successful ; at  least,  which  have  proved 
most  successful  in  his  hands. 

These  may  be  divided  into  two  classes  : one,  in  which 
the  emulsion  is  formed  in  collodion  and  the  plate  coated 
and  then  washed ; the  other,  in  which  the  same  emulsion 
is  dried  and  washed,  and  re- dissolved,  the  plate  being 
coated  with  the  emulsion  as  required.  With  the  former 
method,  unless  the  bromide  is  in  excess,  the  emulsion  has 
to  be  prepared  from  time  to  time  as  required,  and 
if  the  bromide  be  in  excess  the  emulsion  works  very 
slowly.  With  the  latter  process,  where  it  is  washed,  the 
emulsion  will  keep  any  time,  always  supposing  no  decom- 
position sets  up  in  the  pyroxyline.  We  have  ourselves 
kept  some  emulsions  of  this  class  seven  years  which  are 
just  as  sensitive,  if  not  more  sensitive,  than  when  freshly 
prepared. 

ui€  plain  collodion  with  which  the  emulsion  is  to  be  made 


THE  PLAIN  COLLODION. 


35 


shall  be  first  dealt  with,  distinguishing  the  qualities  neces- 
sary for  the  unwashed  and  for  the  washed  emulsion. 

Some  emulsion  workers  have  laid  it  down  as  an  axiom 
that  the  pyroxyline  for  the  two  processes  should  differ, 
while  others  declare  that  this  is  unnecessary.  Again,  some 
declare  that  to  gain  good  density  the  pyroxyline  should 
contain  a percentage  of  organic  matter,  presumably  to  be 
capable  of  acting  on  the  silver  bromide  during  development, 
or  by  forming  some  definite  compound  with  silver.  Our 
own  experience  is,  that  for  securing  density,  organic  matter 
is  unnecessary,  though  it  may  improve  sensitiveness ; and 
we  have  found  in  some  instances  that  density  was  abso- 
lutely impossible  to  attain  where  organic  matter  was  pre- 
sent. We  shall  touch  on  the  question  of  density  of  the 
image  further  on. 

If  a preservative  be  used  as  a sensitizer,  there  can  be 
no  doubt  that  a collodion  should  be  used  which  is  as 
porous  as  possible,  to  enable  it  to  surround  the  particles  of 
the  sensitive  salt.  This  porosity  has  also  another  advan- 
tage, which  is,  that  when  the  preservative  is  washed  off 
previous  to  development,  the  sensitive  salt  is  immediately 
accessible  to  the  action  of  the  developer.  It  is  such  a 
collodion  that  is  recommended  for  dry  plates  prepared 
with  the  aid  of  the  bath,  more  particularly  in  the  collodio- 
albumen  process,  though  in  this  process  the  sensitive  6alt 
is  more  especially  contained  in  the  albumen,  and  it  is 
therefore  necessary  that  a fair  quantity  of  the  latter  should 
be  on  the  plate,  which  is  accomplished  by  this  porosity  of 
the  collodion  film.  For  any  emulsion  process,  we  consider 
a horny  collodion  objectionable,  owing  to  the  difficulty 
that  exists  in  making  the  developer  penetrate  through  the 
film.  A horny  collodion  has,  however,  one  advantage  in 
that  it  acts  as  a varnish  to  exclude  the  air  from  the  sensi- 
tive salts  enclosed  within  it.  In  the  following  formulae 
which  are  given  for  the  preparation  of  the  pyroxylines,  one 
will  produce  an  ordinary  tough  film,  and  the  other  a fairly 
porous  film,  and  consequently  a rather  powdery  pyroxyline. 


36 


THE  PLAIN  COLLODION. 


The  solvents  of  the  pyroxyline  should  be  as  pure  as 
practicable  to  secure  the  maximum  of  sensitiveness,  and 
this  has  been  shown  to  be  the  case  by  that  indefatigable 
experimentalist,  Mr.  H.  Berkeley,  in  a communication  he 
made  to  the  British  Journal  of  Photography . There  is, 
for  instance,  no  doubt  that  when  methylated  alcohol  is 
used,  there  may  be  a lack  of  sensitiveness,  and  even  a 
production  of  fog.  The  ordinary  methylated  ether,  how- 
ever, will  be  found,  as  a rule,  to  be  sufficiently  pure. 


CHAPTER  VI. 


PYROXYLINE. 


The  following  formulas  for  the  preparation  of  the  various 
kinds  of  pyroxyline  will  he  useful  to  note.  The  first  is 
taken  from  u Instruction  in  Photography,”  and  is  re- 
printed here  as  being  convenient  for  reference.  u The 
general  directions  given  are  those  recommended  by 
Hardwich. 

1$£  Process, 

Take — 

Sulphuric  acid  (1*842)  at  158  Cent.  18  fluid  ounces. 

Nitric  acid  (1*456) 6 „ „ 

Water  4f  „ „ 


Or, 

Sulphuric  acid  ( 1*842)  18  fluid  ounces. 

*Nitric  acid  (1*42) 6^  „ „ 

Water  4J  „ „ 

The  water  is  first  poured  into  a strong  glazed  porcelain 
basin,  the  nitric  acid  next  added,  and  lastly,  the  sulphuric 
acid.  The  mixture  is  well  stirred  with  a glass  rod.  The 
temperature  will  now  be  found  to  be  somewhere  about 


* The  nitric  acid  ot  the  strength  given  in  this  formula  is  cheaper  than 
that  of  the  first,  and  is  a standard  strength,  hence  it  is  recommended  for 
economy’s  sake  to  use  it. 


38 


PYROXYLINE. 


190°.  It  must  Ibe  allowed  to  cool  to  150°,  and  this  tem- 
perature must  be  maintained  on  a water-bath.  A dozen 
balls  of  cotton  wool,  weighing  about  thirty  grains  (which 
have  previously  been  well  washed  in  carbonate  of  soda 
and  thoroughly  dried),  should  now  be  immersed  separately 
in  the  fluid  with  the  aid  of  a glass  spatula.  Each  ball 
should  be  pressed  separately  against  the  side  of  the  basin, 
till  it  is  evident  that  the  acids  have  soaked  into  the 
fibre.  Care  must  be  taken  that  each  one  is  immersed  at 
once.  F ailing  this,  a different  chemical  combination  takes 
place,  and  nitrous  fumes  are  given  off,  and  the  success  of 
the  operation  is  vitiated.  Immersing  the  dozen  balls  will 
take  about  two  minutes.  The  basin  should  after  this  be 
covered  up  for  about  ten  minutes.*  At  the  expiration  of 
this  time  the  whole  of  the  cotton  should  be  taken  up  be- 
tween two  glass  spatulas,  and  against  the  sides  of  the 
clean  porcelain  capsule  as  much  of  the  acids  as  possible 
should  be  squeezed  out.  The  cotton  should  then  be 
dashed  into  a large  quantity  of  water,  and  washed  in 
running,  or  frequent  changes  of,  water  for  twenty-four 
hours.  Finally,  when  it  shows  no  acid  reaction  to  blue 
litmus  paper,  it  is  dried  in  the  sun  or  on  a water-bath. 


2nd  Frocess. 


Sulphuric  acid  (1*842) 
Dried  nitrate  of  potash 
Water 

Best  cotton  wool  ... 


...  6 fluid  ounces 

...  3£  ounces  (Av.) 

...  1 fluid  ounce 

...  60  grains 


Mix  the  acid  and  water  in  a porcelain  vessel,  then  add 
the  nitrate  (which  has  previously  been  dried  on  a metal 
plate  to  about  250°,  and  then  pulverized)  by  degrees,, 
stirring  with  a glass  rod  until  all  lumps  disappear,  and  a 


* This  prevents  the  access  of  the  air  to  the  fluid,  and  prevents  the  absorp- 
tion of  oxygen,  and  consequent  formation  of  the  nitrous  fumes. 


PYROXYLINE. 


39 


transparent  viscous  fluid  is  obtained.  This  will  occupy 
several  minutes. 

The  whole  of  the  cotton  wool  must  now  be  separated 
into  balls  the  size  of  a walnut,  and  immersed  as  stated  in 
the  first  process,  care  being  taken  that  the  temperature  is 
kept  up  to  150°.  The  cotton  is  then  left  ten  minutes, 
and  washed  as  before.  Mr.  Hardwich  states  that  the 
chances  of  failure  in  this  process  11  are  very  slight  if  the 
sulphuric  acid  be  sufficiently  strong,  and  the  sample  of 
nitrate  not  too  much  contaminated  with  chloride  of 
potassium.”  If  failure  occur  through  the  cotton  dissolv- 
ing in  the  acid,  a drachm  less  water  must  be  used. 

In  both  processes  the  operation  may  be  conjectured  to 
be  successful  if  the  cotton  tear  easily  in  the  hand,  and  if 
the  original  lumps  cannot  be  easily  separated.  Should 
nothing  but  fragments  of  the  lumps  be  detected,  it  is  pro- 
bable (if  the  acids  used  have  been  of  the  strength  given 
above)  that  the  temperature  has  been  allowed  to  fall.  If 
dried,  the  pyroxyline  should,  when  pulled,  break  up  into 
little  bits,  and  should  not  resemble  the  original  cotton  in 
texture. 

The  weight  of  good  pyroxyline  should  be  greater  than 
the  original  cotton  by  about  25  per  cent. 

If  the  acids  used  are  too  strong,  the  pyroxyline  will  be 
much  heavier  than  this  percentage,  and  will  make  a thick 
glutinous  collodion ; whereas,  if  the  acids  have  been  too 
diluted,  it  will  probably  weigh  less  than  the  original 
cotton,  and  will  yield  a collodion  adhering  firmly  to  the 
plate,  and  giving  negatives  of  too  great  softness : any 
small  particles  of  dust  that  may  fall  on  the  glass  will  form 
transparent  marks.  The  formula  given  steers  between 
the  two  extremes.  There  is  a large  proportion  of 
sulphuric  acid  in  the  above  solution  of  acids,  and  it  is 
to  this  that  is  probably  due  the  tough  film  which  the 
resulting  collodion  gives.  In  fact,  the  excess  of  sulphuric 
acid  partially  “ parchmentizes  ” the  cotton. 

The  late  Mr.  G.  W.  Simpson  described  a modification 


40 


P YROXY  LINE. 


of  Hardwich’s  formula,  which  has  given  excellent  result 
in  our  hands  ; the  mode  of  procedure  is  the  same  as  that 
described  above.  The  following  is  an  extract  taken  from 
the  Photographic  News  : — ■“  As  Hardwich’s  formula  for 
the  manfacture  of  pyroxyline  is  given,  we  may  add  a 
caution  derived  from  our  own  experience  with  it.  In  our 
practice,  we  found  it  to  contain  too  large  a proportion  ot 
water,  and  our  experiments  with  it  issued  in  something 
like  fifty  per  cent,  of  failures,  the  cotton  dissolving  almost 
entirely  in  the  acids.  We  may  add  a formula  which 
we  have  found  to  give  an  excellent  sample  of  soluble 
cotton  for  emulsion  work,  the  collodion  holding  the 
particles  of  silver  salt  well  in  suspension,  and  giving  a 
homogenous  film,  adhering  well  to  the  glass.  The  for- 
mula we  subjoin  has  the  advantage  that  the  acids  are 
readily  obtainable  in  commerce  of  the  strength  we  men- 
tion, and  are  consequently  cheap.  Six  measured  parts  of 
sulphuric  acid  1*840  (ordinary  commercial  oil  of  vitriol 
will  serve),  and  four  measured  parts  of  nitric  acid  1*360. 
This  is  the  strength  of  acid  commonly  sold  as  a pure 
nitric  acid.  In  three  measured  ounces  of  the  mixed  acids, 
one  drachm  of  cotton  wool  should  be  immersed  at  a 
temperature  of  150°  Fah.,  using  a water  bath  to  maintain 
that  temperature  for  ten  minutes,  when  the  cotton  should 
be  removed  and  washed  at  once  in  a large  quantity  of 
water.  India-rubber  gauntlets  should  always  be  used 
when  making  pyroxyline.” 

In  the  next  formulas  the  proportion  of  sulphuric  acid  is 
diminished,  and  in  consequence  we  get  a pyroxyline  which 
is,  if  anything,  deficient  in  tenacity.  For  dry  plate 
processes  with  the  bath,  however,  it  is  excellent,  and 
will  be  found  of  great  use  in  emulsion  processes  in  which 
a preservative  is  used.  The  formulas  are  those  given  by 
Warnerke  in  a communication  to  the  Photographic  Society 
of  Great  Britain  made  in  1876. 

His  modus  operand 7,  based  on  a communication  made 
to  him  by  Colonel  Stuart  Wortley,  is  the  following  : — 


PYROXYLINE. 


41 


100  grains  of  the  finest  cotton-wool  are  put  into  a porce- 
lain jar,  and  30  grains  of  gelatine  dissolved  in  the  smallest 
amount  of  hot  water  are  added.  By  pressing  it  with  a 
wooden  stick,  all  the  cotton  will  he  uniformly  impregnated. 
It  is  subsequently  very  thoroughly  dried  before  the  fire. 

Nitric  acid  (sp.  gr.  1*450)...  ...  4 fluid  ounces 

Water  12J  drachms 

Sulphuric  acid  (sp.  gr.  1*840)  ...  6 fluid  ounces 

are  mixed  in  the  order  named.  An  arrangement  is  pro- 
vided to  keep  the  temperature  of  the  mixture  uniformly 
at  158°  Fahr.  The  dried  gelatinized  cotton,  weighing 
now  about  1 30  grains,  is  immersed  in  the  mixed  acids, 
and  left  in  twenty  minutes.  After  the  lapse  of  this  time 
the  acids  are  pressed  out,  and  the  pvroxyline  quickly 
transferred  to  a large  vessel  of  water.  Washing  and 
drying  follow.  Colonel  Stuart  Wortley  recommended 
also  a second  mode.  Gelatine,  instead  of  being  added  to 
the  cotton,  is  dissolved  in  the  water  figuring  in  the  formula 
of  the  acids,  and  ordinary  dry  cotton  immersed  in  the 
mixture  of  gelatinized  acids. 

Mr.  Warnerke  states  that  before  washing  the  gelatin- 
ized emulsion  a remarkable  increase  of  intensity  and  sensi- 
tiveness is  obtained.  After  washing,  the  difference  is 
less  striking,  but  still  sufficiently  marked  to  prove  the 
new  pyroxyline  to  be  a very  decided  improvement. 

Mr.  Warnerke  states  that  pyroxyline  giving  extraordin- 
ary density  can  be  prepared  from  the  raw  hemp.  Collo- 
dion from  hemp-pyroxyline  is  red  in  colour,  and  very 
fluid ; but  the  insoluble  deposit  is  very  considerable ; it 
also  requires  stronger  acids.  It  is  worth  remarking  that 
the  strength  of  acids  must  vary  with  different  samples 
of  fibres,  even  in  the  case  of  different  cottons.  A very 
good  pyroxyline  can  be  prepared  from  Whatman’s  hand- 
made paper,  instead  of  the  cotton  in  the  above  formula, 
which,  being  sized  with  gelatine,  offers  a ready-made 
material,  suitable  for  making  gelatinized  pyroxyline.” 


42 


PYROXYLINE. 


The  great  difficulty  in  this  formula  is  the  easy  solu- 
bility of  the  cotton  at  the  high  temperature.  A reduction 
in  the  amount  of  water  will  prevent  this.  Pyroxyline 
from  ordinary  cotton  can  be  prepared  by  the  same  formula , 
and  gives  a powdery  film.  The  writer  disagrees  with 
Mr.  Warnerke  as  to  the  desirability  of  this  state  of  the 
film  for  washed  emulsion  when  used  on  rigid  supports, 
such  as  glass,  but  the  limpidity  given  by  it  to  the  collo- 
dion is  very  desirable  in  the  case  of  a flexible  support, 
such  as  that  with  which  Mr.  Warnerke’s  name  is  asso- 
ciated. 

Mr.  J.  Traill  Taylor  gave  an  excellent  description  of 
the  method  to  be  adopted  for  making  any  pyroxyline 
suitable  for  emulsion.  He  says  : 

a Pyroxyline  possessing  the  requisite  qualities  is  by  no 
means  so  easily  obtained  as  the  ordinary  sort.  Precipi- 
tated pyroxyline  forms  at  once,  if  properly  made,  even 
from  the  cheapest  materials,  not  only  a perfect  substitute 
for  the  high-priced  samples  usually  employed,  but  for 
some  purposes  gives  an  absolutely  superior  result. 

u We  commenced  with  a sample  of  pyroxyline  which 
is  sold  at  16s.  the  pound ; it  is  very  soluble,  and  gives 
little  or  no  residue,  hut  is  of  little  use  for  emulsion  work. 
Of  this  400  grains  were  dissolved  in  a mixture  of  10  ounces 
of  methylated  ether,  s.g.  *730,  and  10  ounces  of  ordinary 
methylated  spirit,  retailed  at  5s.  a gallon.  The  resulting 
collodion,  after  standing  for  a couple  of  days,  though  very 
thick,  as  might  be  expected,  was  tolerably  clear,  except 
for  the  presence  of  a few  floating  specks  and  particles  of 
dust,  which  were  removed  by  passing  it  through  muslin. 
This  was  poured  into  cold  water,  and  the  precipitate,  when 
washed  and  thoroughly  dried,  weighed  368  grains,  or 
exactly  8 per  cent,  less  than  the  original  cotton.” 

After  stating  that  it  is  a wrong  plan  to  pursue  to  pour 
the  collodion  gently  on  the  water,  the  writer  continues  : 
u The  proper  course  to  follow,  as  laid  down  by  M. 
Chardon,  is  just  the  reverse  of  this ; the  collodion  is 


PYROXYLINE. 


43 


poured  into  the  water  in  a thin  stream — preferably  from 
a height — and  is  stirred  vigorously  during  the  time  of 
pouring,  and  for  a minute  or  two  afterwards.  By  this 
means  it  is  broken  up  into  innumerable  drops,  each  of 
which,  immediately  it  comes  into  contact  with  the  water, 
is  converted  into  a distinct  spongy  mass  or  flock,  being 
deprived  almost  instantaneously  of  its  ether  and  alcohol. 
The  stirring  is  continued  as  long  as  the  mass  exhibits 
any  cohesive  tendency,  and  when  it  feels  harsh  and  firm 
to  the  touch  it  may  be  known  that  the  removal  of  the 
solvents  is  complete.  The  water  is  then  changed,  the 
cotton  passed  through  a cloth,  and  dried.” 

Mr.  J.  T.  Taylor  further  says  : — u Except  in  physical 
conditions,  we  cannot  find,  with  a given  sample  of  cotton, 
that  it  is  of  much  importance  whether  the  precipitation 
is  performed  in  hot  or  cold  water.” 

In  order  to  avoid  waste  in  washing  and  drying,  it  will 
be  found  convenient  to  employ  a conical  bag  fixed  upon 
a hoop  of  thin  cane.  When  the  precipitation  is  complete, 
the  whole  of  the  contents  of  the  vessel  are  transferred  to 
the  washing  bag,  and  after  passing  two  or  three  pints  of 
water  through  to  remove  the  last  traces  of  ether  and 
alcohol,  the  mass  of  cotton  is  squeezed  as  dry  as  possible, 
and  may  then  be  removed  as  a lump  ; it  is  then  broken 
down  with  the  fingers  or  a spatula  upon  a clean  porcelain 
dish,  and  dried  at  a gentle  heat  on  a water  bath.  When 
quite  dry,  it  should  present  the  appearauce  of  light  flakes 
of  pure  white,  and  easily  reduced  to  powder.  It  dis- 
solves as  rapidly  as  ordinary  pyroxyline,  and  if  carefully 
prepared  gives  at  once  a perfectly  bright  solution  of  a 
faint  yellow  tinge.  It  gives  upon  the  glass  a hard,  smooth 
film,  non-contractile,  and  yet  differing  totally  from  the 
so-called  powdery  films  commonly  spoken  of  in  connec- 
tion with  dry  plates. 

In  the  same  article  a reference  is  made  to  M.  Blondeau’s 
analysis  of  preciptated  cotton,  in  which  it  is  stated  that 
8 per  cent,  of  water  is  taken  into  combination.  This 


44 


PYROXYLINE. 


amount  of  water,  if  it  exist  in  the  cotton,  must  alter  the 
structure  of  the  collodion  in  a marked  way. 

Be  this  as  it  may,  precipitated  cotton  does  gives  a very 
fine  film ; hut  we  are  inclined  to  think  that  part  of  the 
effect  is  produced  by  the  alcohol  being  eliminated  from 
it  en  masse , and  carrying  with  it  that  constituent  of  the 
pyroxyline  which  is  soluble  in  the  alcohol.  This  will  be 
seen  to  be  the  case  in  which  a finished  emulsion  was 
washed  in  alcohol ; the  resulting  film  having  much  re- 
semblance to  that  of  M.  Chardon’s. 

The  amateur  will  probably  find  it  most  convenient 
to  purchase  ordinary  pyroxyline  from  some  respectable 
dealer,  who  is  a manufacturer  of  good  collodion,  instead 
of  making  it  himself,  for  of  all  processes  connected  with 
photography,  that  of  making  pyroxyline  is,  perhaps, 
the  most  unpleasant  and  hurtful  to  the  health  and 
clothes.  The  stains  on  the  latter  from  nitric  acid  or 
sulphuric  acid  can  never  be  eliminated,  unless  the  acid  be 
immediately  neutralized,  and  sulphuric  acid  will  rapidly 
eat  through  any  organic  texture,  unless  it  be  either 
washed  thoroughly , or  an  alkali  be  applied. 

As  regards  the  character  of  the  solvents,  there  is  little 
to  be  said  in  regard  to  the  ether.  That  of  a specific 
gravity  of  *730  is  generally  employed,  and,  if  it  be,  an 
alcohol  of  low  specific  gravity  should  be  employed,  such 
as  *812;  whereas  if  the  ether  have  a specific  gravity  of 
*720,  a specific  gravity  of  *820  for  the  alcohol  is  allowable. 

After  the  plain  collodion  (see  next  page)  is  mixed,  it 
should  be  allowed  to  settle.  No  matter  what  pyroxyline 
be  employed,  it  will  invariably  be  found  that  there  is 
some  floceulent  matter,  too  fine  for  filtering  out,  which, 
if  not  got  rid  of,  is  one  great  cause  of  spots  on  emulsion 
plates,  and  therefore  every  effort  should  be  made  to  pre- 
vent its  finding  its  way  into  the  emulsion.  The  collodion 
should,  therefore,  be  allowed  to  remain  undisturbed  for  a 
week  or  two,  to  allow  these  fine  particles  to  deposit. 


CHAPTER  VII. 


PREPARATION  OF  AN  EMULSION. 

It  is  unnecessary  to  enter  into  the  history  of  the  emulsion 
processes ; but  it  may  not  be  uninteresting  to  note  that  the 
first  published  formula  lor  a collodio-bromide  emulsion 
was  by  Messrs.  Bolton  and  Sayce,  in  September,  1864. 

Though  not  following  an  historical  order,  we  have 
thought  it  best  to  give  the  method  of  preparing  an  emul- 
sion which  can  be  followed  in  nearly  all  modifications  of 
the  process ; and  to  make  it  clearer,  a definite  formula 
has  been  made  use  of,  giving  an  emulsion  which  is  very 
simple  and  clean  working,  and  though  not  boasting  any 
extraordinary  sensitiveness,  is  yet  more  sensitive  than  any 
bath  dry-plate  process  with  which  the  writer  is  ac- 
quainted. 

The  plain  collodion*  is  made  as  follows 

Alcohol  *820  . 10  ounces 

Ether  *730  ...  ...  ...  20  „ 

Pyroxy line  (ordinary)...  ...  400  grains 

* If  the  plain  collodion  supplied  by  dealers  be  used,  it  must  be  recollected 
that,  as  a rule,  it  contains  about  5 grains  of  pyroxyline  to  the  ounce  after 
the  iodizer  has  been  added.  The  formula  may  be  taken  to  be  as  foUows: — 

Alcohol 20  ounces 

Ether 40  „ 

Pyroxyline  400  grains 

The  bromide  and  silver  must  be  added  according  to  the  grains  of  pyroxyline, 
not  according  to  the  amount  of  solvents  in  which  it  is  dissolved. 


46 


PREPARATION  OF  AN  EMULSION. 


We  will  suppose  that  we  are  going  to  prepare  an  emul- 
sion which  will  make  up  to  twenty  ounces.  When  it  is 
evaporated,  washed,  and  re-emulsified,  each  ounce  of 
washed  emulsion  should  contain  about  5 grains  of  pyroxy- 
line,  and,  therefore,  we  must  take  one-fourth  of  the  collo- 
dion made  up  as  above  {vide  Note  page  45),  which  will 
be  7£  fluid  ounces.  It  is  proposed  that  each  fluid  ounce  of 
re-dissolved  emulsion  shall  contain  about  15  grains  of 
silver  bromide.  The  salt  we  propose  to  use  is  zinc  bro- 
mide, and  we  find  that  about  10  grains  of  this  salt  are 
necessary  for  this  purpose.  To  our  ounces  of  collodion, 
therefore,  we  must  add  at  some  time  or  another  200  grains 
of  this  salt.  Two  portions  of  100  grains  each  are  weighed 
out : one  is  dissolved  in  the  smallest  quantity  possible  of 
alcohol,  and  4 or  5 drops  of  concentrated  nitric  acid  are 
added  to  it  to  render  innocuous  any  oxide  or  other  im- 
purity that  may  be  present.  This  is  then  added  to  the 
collodion.  The  other  100  grains  are  similarly  dissolved, 
but  a larger  proportion  of  nitric  acid  added,  viz.,  10  drops. 
This  is  kept  in  a test-tube  ready  for  use.  We  next  require 
300  grains  of  silver  nitrate  to  saturate  the  zinc-bromide, 
and  to  allow  3 grains  in  excess  for  each  ounce  of  the  concen- 
trated collodion.  As  this  will  probably  be  about  1 1 ounces 
by  the  time  the  additions  are  made,  330  grains  of  silver 
nitrate  (which  has  previously  been  pounded  up  in  an 
agate  mortar,  or  the  crystals  of  which  have  been  crushed 
with  a glass  stopper  on  a thick  glass  plate)  are  weighed 
out.  This  amount  is  then  placed  in  a large  test-tube, 
with  5 dr.  of  water,  and  warmed : a perfect  solution 
ought  to  result.  Ten  drops  of  nitric  acid  are  next 
added  to  it.  In  another  test-tube  1^  ounce  of  alcohol 
(•820  to  *830)  are  boiled,  and  poured  upon  the  dissolved 
silver.  The  two  fluids  may  not  mix  at  first,  but  by 
pouring  them  from  one  test-tube  to  another  this  is  readily 
accomplished.  The  collodion  is  now  placed  in  a glass 
jar,  and  a 6tirring-rod  placed  ready  to  hand.  It  is  usually 
insisted  that  the  subsequent  operations  should  be  con- 


PREPARATION  OF  AN  EMULSION. 


47 


ducted  in  the  dark  room.  This  exclusion  of  light  is  quite 
unnecessary  (as  the  writer  has  practically  proved),  owing 
to  the  presence  of  the  nitric  acid,  which  renders  the  sub- 
bromide  inert  as  fast  as  it  is  formed  by  the  action  of 
light.  The  test-tube  containing  the  silver  is  now  taken 
in  the  left  hand,  and  the  stirring-rod  in  the  right,  and 
three-quarters  of  the  silver  nitrate  solution  is  poured,  drop 
by  drop,  into  the  collodion,  which  is  kept  in  brisk  agita- 
tion by  the  glass  rod.  The  silver  solution  is  then  placed 
on  one  side,  and  the  dissolved  bromide  solution  taken  in 
the  left  hand.  All  the  latter  is  now  added  drop  by  drop, 
and  then  the  remainder  of  the  silver  solution  in  a similar 
manner.  Some  of  the  silver  salt  is  sure  to  be  found 
crystallized  on  the  edge  and  sides  of  the  test-tube.  This 
is  re-dissolved,  as  before,  in  a little  water  and  half  an  ounce 
of  alcohol,  and  added  with  the  same  precautions.  If  the 
above  details  have  been  carefully  carried  out,  the  colour 
of  a candle  or  gas-flame,  when  viewed  through  the  liquid 
which  runs  down  the  inside  of  the  glass  jar  after  agitation, 
should  appear  of  a deep  orange  approaching  to  a ruby 
tint.  When  in  this  condition,  it  may  be  judged  that  it 
has  been  rightly  prepared.  With  the  glass  rod  a drop  or 
two  of  the  emulsion  should  be  dropped  on  to  small  strips 
of  glass,  and  examined  by  daylight  for  structure,  &c. 
When  viewed  through  a window,  the  principal  part  of  the 
light  transmitted  should  be  orange.  A little  potassium 
chromate  should  be  dropped  on  to  the  emulsion  on  the 
plate,  and  a bright  red  colour  will  show  that  the  silver  is  in 
excess,  which  is  what  is  required  in  our  case.  If  this 
colouration  be  absent,  it  will  indicate  that  the  soluble  bro- 
mide is  in  excess,  which,  in  some  modifications  of  the  same 
process,  is  what  may  be  desired.  The  emulsion  must  next 
be  decanted  off  into  a bottle  capable  of  containing  at  least 
double  the  amount  of  fluid — that  is,  at  least  20  ounces — 
and  it  should  then  be  shaken  for  ten  minutes.  It  may 
now  be  put  on  one  side  for  from  sixteen  to  twenty-four 
hours,  when  it  will  be  ready  for  the  next  operation. 


48 


PREPARATION  OF  AN  EMULSION. 


We  will  now  give  a slightly  different  method  for  mixing 
the  silver  and  the  soluble  bromide,  which  has  been 
adopted  by  some  people,  amongst  others  by  Warnerke,  to 
whom  the  writer  is  much  indebted  for  information  on 
various  points. 

A couple  of  corks,  D and  E (fig.  8),  which  should  fit  the 
necks  of  the  bottles  A and  B,  are  bored  with  holes  just 
wide  enough  to  admit  a glass  tube,  C,  which  has  a diameter 
of  bore  of  about  one-eightli  of  an  inch.  The  whole  of  the 
bromide  is  dissolved  in  half  the  amount  of  collodion  used, 
and  placed  in  the  bottle  A,  which  (like  B)  should  have 
sufficient  capacity  to  hold  double  the  amount  of  emulsion 
to  be  made  up  ; the  cork,  D,  with  the  glass  rod,  C,  should 


Fig.  8.  Fi9 • 9- 


next  be  fitted  into  it.  Into  the  other  bottle,  B,  the  silver 
nitrate  solution  is  added  to  the  collodion,  sufficient  alcohol 
and  water  being  used  to  keep  it  in  thorough  solution.  The 
bored  cork,  E,  is  then  fitted  into  the  neck,  and  the  far  end 
of  the  glass  tube  deftly  inserted,  and  the  tops  of  the  bottles 
brought  close  together.  The  hands  then  grasp  the  necks, 
and  the  contents  are  shaken  up,  when  a little  of  B gradually 
finds  its  way  into  A.  The  positions  of  the  bottles  are 


PREPARATION  OF  AN  EMULSION. 


49 


tlien  reversed,  and  a little  of  the  contents  of  A shaken 
into  B ; when  each  of  the  bottles  seems  to  contain  emulsion 
equally  dense,  the  whole  of  one  bottle  is  gradually  caused 
to  drop  into  the  other,  and  by  this  means  a perfect  emulsion 
is  obtained.  The  emulsion  may  be  made  even  more 
rapidly  by  adopting  the  contrivance  shown  in  fig.  3,  in 
which  there  are  two  tubes,  one  always  acting  as  an  inlet 
for  air,  whilst  through  the  other  the  collodion  finds  a 
passage.  In  this  case,  narrow  bored  tubes  are  advisable, 
certainly  not  greater  than  one-eighth  of  an  inch. 

Now  it  has  been  said  that  in  sixteen  to  twenty-four 
hours  the  emulsion  will  be  ready  for  pouring  out.  This 
statement  is  true  for  the  particular  emulsion  described, 
but  it  is  not  necessarily  true  for  emulsions  when  other 
soluble  bromides  are  employed.  Thus  we  find  that 
Col.  Wortley  stated  to  the  Photographic  Society  of  Great 
Britain,  on  14th  March,  1876,  that  the  following  is  the 
time  necessary  for  emulsions  made  with  the  following 
soluble  bromides  to  ripen  : — 

hours 
77 

?7 
?? 

77 
77 
?? 

77 
77 
77 
77 
77 
77 

It  will  be  noticed  that  Colonel  Wortley  gives  zinc 
emulsion  ten  and  a-half  hours,  as  the  time  for  attaining 
the  maximum  se  nsiti veness.  The  discrepancy  is  probably 
dne  to  the  greater  viscosity  of  the  collodion  employed  in 


Manganese 

• • • 

...  7* 

Cadmium 

• • • 

...  9 

Strontium 

... 

...  10 

Magnesium 

,,, 

...  10 

Zinc 

• • • 

...  10* 

Cerium  ... 

...  14 

Potassium 

...  14 

Cinchonine 

...  15 

Sodium... 

... 

...  15* 

Calcium 

...  17 

Ammonium 

...  17* 

Uranium 

...  17* 

Barium... 

• • • 

...  19 

50 


PREPARATION  OF  AN  EMULSION. 


the  one  case  as  compared  with  the  other.  The  list,  how- 
ever, is  useful  as  showing  the  comparative  times  that 
should  be  allowed  for  ripening.  We  might  here  leave  the 
emulsion  as  ready  for  coating  plates  after  proper  dilution, 
but  we  will  further  suppose  that  it  is  to  be  washed,  a modi- 
fication introduced  by  Mr.  Wr.  B.  Bolton,  one  of  the  origi- 
nators of  the  collodio-bromide  emulsion  process.  The  first 
step  to  be  taken  is  to  allow  the  solvents  to  evaporate. 

Evaporating  the  Solvents . — An  emulsion  generally  may 
be  prepared  in  the  afternoon  of  one  day,  well  shaken 
before  leaving  the  laboratory,  and  on  the  next  day,  about 
noon,  the  emulsion  will  be  ready  for  drying.  The  mode 
adopted  by  the  writer  is  as  follows  : — The  emulsion  is 
poured  out  into  a flat  dish,  to  a depth  of  a quarter  of  an 
inch,  and  placed  in  a dark  room,  the  temperature  of  the 
latter  being  raised,  if  possible,  to  70°.  For  the  ten 
ounces  of  emulsion  made,  a porcelain  dish,  about  14  by 
12  by  three-quarters  of  an  inch  deep,  is  required. 

After  a short  interval  it  will  be  found  that  a skin  forms 
on  the  surface  of  the  collodion ; this  is  broken  up  with  a 
glass  rod,  and  a fresh  liquid  surface  given  to  it.  Every 
half  hour  the  whole  of  the  emulsion  is  thoroughly  well 
stirred  up,  till  it  begins  to  break  into  lumps,  when  it  can 
be  left  a short  time,  for  the  solvents  still  further  to 
evaporate.  It  is  ready  for  the  first  washing  when  the 
lumps  require  a little  force  to  break  them  up — in  other 
words,  when  they  are  about  the  same  consistency  as  a 
collodion  film  before  dipping  into  the  bath.  The  mass  is 
then  removed  to  a glass  beaker,  and  covered  with 
distilled  water.  At  this  point  we  have  a good  test  as  to 
whether  the  evaporation  of  the  solvents  has  been  con- 
tinued far  enough.  If  only  a few  of  the  lumps  rise  to 
the  surface,  the  evaporation  has  been  sufficient ; if,  on 
the  other  hand,  the  majority  float  on  the  surface  of  the 
water,  it  has  not  been  continued  long  enough.  The  reason 
of  this  tendency  of  the  lumps  to  rise  to  the  surface  is  due 
to  the  light  specific  gravity  of  the  ether  and  alcohol,  which, 


PREPARATION  OF  AN  EMULSION. 


51 


even  with  the  weight  of  the  solid  matter,  is  not 
sufficient  to  counterbalance  the  specific  gravity  of  the 
water. 

This  method  of  eliminating  the  solvents  is,  however, 
wasteful,  and,  if  preferred,  resort  may  he  had  to  distilla- 
tion (see  Appendix) ; hut  this  method  should  not  he 
adopted  unless  all  acid  be  omitted  previous  to  distillation, 
since  boiling  an  emulsion  in  its  presence-  produces  a 
very  horny  film,  and  nitrous  ether  is  formed.  The  acid 
must  he  applied  in  the  first  wash  water.  Let  it  he 
recollected  that  where  the  bromide  is  not  in  excess,  but 
where  there  is  an  excess  of  silver  nitrate , nitric  acid  or  its 
equivalent  must  be  added  to  the  emulsion  itself  ’ or  to  the  wash- 
water  at  some  stage — the  time  of  addition  being  dependent 
on  the  circumstances  already  explained.  rJhe  whole  of  the 
operations  up  to  the  first  washing  may  be  carried  on  in  the  light . 
In  M.  Chardon’s  process,  as  subsequently  given  (page  59), 
it  will  he  seen  how  this  evaporation  of  the  solvents,  pre- 
vious to  washing,  may  he  dispensed  with.  It  is  hardly 
worth  while  to  repeat  the  method  here,  more  particularly 
when,  in  some  respects,  the  above  is  really  superior  to  it ; 
at  least,  so  the  writer  has  found. 

F or  the  above  quantity  of  emulsion,  1 drachm  of  nitric 
acid,  which  will  be  ample  to  secure  freedom  from  fog, 
should  be  dropped  into  the  dish,  and  distilled  water  added. 
After  a couple  of  hours  the  true  washing  may  commence. 

A method  which  we  have  found  to  give  still  better  re- 
sults, if  the  acid  is  omitted  from  the  emulsion,  is  to  wash 
the  pellicle  twice  or  three  times  in  water  till  nearly  all 
excess  of  silver  is  removed,  and  then  to  add  2 drachms 
of  hydrochloric  acid  to  the  next  wash-water  (which 
should  not  be  more  than  10  ounces),  and  then  begin 
to  wash  de  novo.  Mr.  Bedford  first  recommended  this 
plan.  Instead  of  the  hydrochloric  acid,  a solution  of 
bichromate  of  potash,  10  grains  to  the  ounce,  to  which 
a pinch  of  common  salt  has  been  added,  may  be  sub- 
stituted. This  is  an  excellent  method,  since  any  trace 


52 


PKEPAKATION  OF  AN  EMULSION. 


of  bichromate  is  visible  in  the  wash-water.  The  pinch 
of  salt  prevents  the  formation  of  bichromate  of  silver. 

To  wash  the  emulsion  it  may  be  placed  in  a jar  or  jam 
pot,  and  be  covered  with  water  where  it  can  stand  two  or 
three  hours  in  the  dark  without  detriment,  when  it  should 
be  changed.  The  way  in  which  the  washing  can  be  econo- 
mically effected,  as  regards  time,  is  as  follows : — A piece 
of  coarse  calico  which  has  previously  been  washed  in  car- 
bonate of  soda,  and  then  well  rinsed,  and  dried,  is  spread 
over  the  top  of  a second  glass  jar  or  large  jam  pot,  and  the 
contents  of  the  first  thrown  on  to  it.  The  calico  acts  as  a 
strainer,  and  the  solid  pellicle  is  left  on  it.  The  calico  is 
next  taken  up  by  the  sides,  and  the  contents  are  twisted  up 
in  it,  and  as  much  as  possible  of  the  liquid  then  wrung  out. 
The  calico  is  untwisted,  and  a bag  formed  by  tying  up  the 
ends,  to  hold  the  emulsion,  which  is  shaken  up  and  im- 
mersed in  fresh  distilled  water.  After  a quarter  of  an 
hour  the  wringing  operations  are  again  proceeded  with, 
and  this  process  repeated  three  or  four  times.  The  ex- 
pelled water  should  now  be  tested  for  free  silver  nitrate 
by  a drop  of  hydrochloric  acid.  If  it  gives  more  than  a 
slight  milkiness,  such  as  is  produced  by  adding  silver 
nitrate  to  water  containing  a grain  of  common  salt  to  the 
gallon,  it  must  be  washed  till  this  maximum  is  attained. 

Preparing  the  Pellicle  for  Re-emulsifying . — A very  im- 
portant part  of  emulsion  making  is  now  to  be  touched 
upon,  viz.,  getting  rid  of  the  water  held  in  the  pellicular 
mass. 

To  commence  with,  as  much  water  as  possible  should 
be  squeezed  out,  and  then  we  may  proceed  in  one  of  these 
ways. 

1st.  We  may  lay  it  out  flat  on  a piece  of  blotting-paper, 
and  allow  it  to  dry  spontaneously.  2nd.  We  may  put  it  in 
a flat  porcelain  dish,  and  place  it  in  a water  bath,  the 
temperature  of  which  can  never  exceed  212°,  and  thus 
all  moisture  may  be  got  rid  of.  In  this  proceeding 
the  very  greatest  care  is  necessary,  as  the  emulsion  is 


PREPARATION  OF  AN  EMULSION. 


53 


apt  to  become  very  hard  indeed — so  much  so  as  to  be 
scarcely  soluble  ; in  addition  to  which,  it  is  often  apt  to 
blacken  spontaneously.  The  third  method  is  one  which 
we  can  confidently  recommend  for  washed  emulsion, 
being  very  simple,  and  absolutely  improving  its  qualities 
when  re-dissolved.  This  is  simply  to  cover  it  with  recti- 
fied spirit  *820  after  as  much  water  as  possible  has  been 
squeezed  out.  In  an  hour’s  time  the  excess  is  drained 
off,  and  the  pellicle  is  squeezed  in  the  cotton  rag  as 
before.  It  is  then  once  more  covered  with  the  spirit,  and 
left  for  half  an  hour,  when,  after  draining  away  the  super- 
fluous spirit,  it  is  ready  for  re-emulsifying.  If  it  be  desired 
to  keep  the  pellicle  in  a solid  state,  it  will  only  be  neces- 
sary to  expose  it  to  the  air  for  a few  hours,  when  it  will 
be  found  quite  dry. 

It  is  instructive  to  examine  the  washings  from  the  spirit. 
It  will  be  found  that  there  is  a certain  small  quantity  of 
silver  bromide  in  suspension,  which  can  be  filtered  out.  If 
the  spirit  be  distilled  over,  a semi-opaque  liquid  residue 
will  be  left,  having  a very  high  boiling  point,  a strong  and 
very  disagreeable  smell,  and  containing  some  organic  salt 
of  silver,  which  discolours  in  the  light.  It  may  be  said 
that  this  organic  compound  is  necessary  for  density  of 
image ; but  a trial  of  the  emulsion  washed  in  this  way  will 
prove  the  contrary  ; in  addition  to  which,  it  will  be  found 
much  freer  from  spots  than  that  washed  and  dried  by  the 
first  two  methods  indicated  above. 

There  are  some  pyroxylines  which  it  would  be  dangerous 
to  treat  in  this  manner,  since  they  are  soluble,  to  a certain 
extent,  in  absolute  alcohol ; but  it  seems  to  the  writer  that 
any  such  pyroxylines  are  detrimental  when  washed 
coilodio-bromide  emulsion  is  in  question.  If  they  are 
employed,  the  old  method  of  drying  must  be  adopted. 

The  dried  (or  moist  with  alcohol)  pellicle  has  next  to  be 
dissolved  in  its  proper  proportions  of  solvents,  which  are 
about  5 grains  of  pyroxyline  to  every  ounce  of  the  two 
when  mixed.  It  is  better  to  make  it  up  first  to  the  strength 


54 


PREPARATION  OF  AN  EMULSION. 


of  10  grains  of  pyroxyline,  and  then  to  add  the  remaining 
solvents,  since  the  colour  of  the  emulsion  seems  to  be 
better  when  a greater  degree  of  viscidity  is  present  when 
the  pellicle  begins  dissolving.  In  two  or  three  hours  the 
whole  of  the  silver  bromide  should  be  in  suspension.  It 
will  be  found,  however,  that  there  is  an  improvement  in 
the  quality  of  the  film  after  the  lapse  of  a couple  of  days, 
or  even  more.  A plate  should  be  tried,  before  diluting 
down  the  collodion  with  more  ether  and  alcohol,  in  order 
to  test  its  flowing  qualities,  and  to  note  the  opacity  of  the 
film. 

In  our  own  experience  we  like  to  be  able  to  see  the 
light  from  a gas  jet  through  a film  whilst  moist,  but 
which,  when  dried,  is  perfectly  opaque.  In  this  con- 
dition the  film  is  tough,  requires  no  backing,  and  is  always 
capable  of  giving  sufficient  density  by  alkaline  develop- 
ment alone,  without  resort  to  intensification. 

Before  taking  into  use,  it  should  be  filtered  through 
cotton-wool  (see  Chap.  XVI.) 

The  exposure  necessary  for  the  washed  emulsion  already 

f 

described  is  very  constant ; with  a lens  of  aperture 
and  in  a fair  light,  thirty  seconds  will  be  found  to  be  ample 
when  using  the  alkaline  or  ferrous  oxalate  developer. 


CHAPTEE  VIII. 


CAREY  LEA’S  CHLORO-BROMIDE  EMULSION. 


In  the  year  1869,  Mr.  Carey  Lea,  the  able  American 
photographer  and  experimentalist,  brought  forward  what 
is  known  as  the  chloro-bromide  process,  in  which  the  new 
feature  of  the  introduction  of  a chloride  into  a bromide  is 
announced,  b y preference  using  cupric  chloride. 

The  excess  of  silver  employed  by  Mr.  Lea  in  this  pro- 
cess was  very  little  over  that  required  for  the  full  satura- 
tion of  the  bromide  and  chloride,  and  after  keeping 
beyond  a certain  time,  in  the  writer’s  experience  fog  was 
always  present  when  this  formula  was  followed.  Mr.  Lea 
himself  seems  to  have  found  this,  for  in  March  of  1870 
he  introduced  a modification  of  this  process,  which 
enabled  any  amount  of  excess  of  silver  nitrate  to  be  used, 
without  any  danger  of  fog  being  produced  in  develop- 
ment. By  this  modification  the- theoretical  considerations, 
subsequently  worked  out  by  the  writer,  and  already 
pointed  out,  were  fulfilled. 

The  following  is  the  mode  of  preparation  of  Mr.  Lea’s 
emulsion  given  in  Mr.  Lea’s  words : — - 


Collodion 

Ether 

Alcohol  

Pyroxyline ... 

Bromide  of  cadmium 
,,  ammonium 


20  fluid  ounces 

12  .» 

162  grains 


. 320 
. 64 


n 


Add  half  the  alcohol  to  all  the  ether,  and  shake  up 


56  CAREY  lea’s  chloro-bromide  emulsion, 

with  the  pyroxyline  ; throw  the  salts  into  a flask  with  the 
rest  of  the  alcohol,  and  heat  till  dissolved  ; add  to  the 
other  portion,  shake  up  well,  and  place  in  a warm,  light 
place  for  three  weeks  ; it  will  be  better  still  in  two  or 
three  months. 

“This  collodion  will  require  16  grains  to  the  ounce 
of  nitrate  of  silver  to  sensitize  it.  I prefer,  and  always 
use,  fused  nitrate,  and  recommend  it  for  all  collodio- 
bromide  work,  as  much  preferable  to  the  crystallized. 

“ Having  measured  out  the  quantity  of  collodion  to  be 
sensitized,  weigh  out  16  grains  of  very  finely  pow- 
dered nitrate  of  silver  to  each  ounce,  throw  it  into  a test- 
tube  or  flask,  and  pour  over  it  alcohol  of  s.  g.  *820  in 
the  proportion  of  1 drachm  to  each  8 grains  of 
nitrate ; boil  for  a few  minutes,  and  the  nitrate  will 
dissolve ; pour  it  now  in  successive  portions  into  the 
collodion,  shaking  up  well  after  each ; shake  about  five 
minutes  after  the  last  portion  is  added,  and  every  few 
times  thereafter ; use  twenty-four  hours  after  sensitizing. 

“ In  twenty  or  twenty-four  hours  after  sensitizing,  the 
mixture  will  be  in  condition  to  use.  The  difference  of  a 
few  hours  will  not  be  important,  but  it  is  best  not  to 
exceed  twent-four.  If  kept  too  long,  there  will  be 
a disposition  to  fog  in  the  shadows,  and  a want  of 
brilliancy  in  the  whole  picture.  The  higli-lights,  also, 
will  not  have  their  details  well  marked.  The  filtering  is 
best  done  by  putting  a piece  of  soft,  clean  sponge  in  the 
neck  of  a funnel,  and  cutting  a small  circular  filter  of 
close-woven  linen.  The  linen  used  for  making  these 
filters  should  be  boiled  for  an  hour  with  very  weak  caustic 
potash  or  soda,  then  well  washed  in  hot  water  (of  course 
without  soap),  and  dried.  This  plan  of  filtering  will  be 
found  excellent  for  all  sorts  of  photographic  collodions. 
Before  filtering,  the  collodio-bromide  mixture  should  rest 
quiet  for  two  or  three  hours  after  its  last  shaking.” 

For  the  preservative  bath  recommended  by  Mr.  Lea 
(see  page  87). 


CHAPTEE  IX. 


CANON  BEECHEY’S  PROCESS. 


We  have  now  to  put  on  record  a process  which  is  at  once 
simple  and  efficient,  and  the  thanks  of  the  photographic 
public  are  due  to  Canon  Beechey  for  its  explicitness  in 
every  detail.  The  following  is  the  modus  operandi : — 

Take  cadmium  bromide  (anhydrous)  400  grains 
Alcohol  (*805)  10  ounces 

and  allow  the  mixture  to  stand.  Decant  carefully,  and 
add  80  minims  of  strong  hydrochloric  acid. 

Take  of  the  above  solution...  ...  \ ounce 

Absolute  ether  (*720)  ...  ...  9 drachms 

Pyroxyline  (as  above)  ...  10  to  12  grains 

To  sensitize  this,  dissolve  40  grains  of  silver  nitrate  in 
an  ounce  of  alcohol  (*820  sp.  gr.)  The  best  method  of 
effecting  this  is  to  pound  up  the  silver  nitrate  in  an  agate 
mortar,  and  to  take  only  a quarter  of  the  alcohol,  and 
boil  it  in  a test-tube  containing  the  silver  salt.  The 
alcohol  will  become  slightly  brown  (due,  probably,  to  the 
formation  of  a fulminate  of  silver),  and  should  be  decanted 
off  into  a bottle  containing  the  collodion.  The  remaining 
silver  should  be  dissolved  up  in  a similar  manner,  the 
ounce  of  alcohol  being  just  sufficient  to  effect  solution. 


58 


CANON  BEECHEY’S  PROCESS. 

Between  each  addition  of  the  silver  nitrate  the  collodion 
should  be  well  shaken.  When  the  final  addition  is  made, 
the  emulsion  should  be  very  smooth,  and  rather  thick. 
When  poured  upon  a strip  of  glass  plate  it  will  appear 
transparent  by  transmitted  light,  but  after  keeping  twenty- 
four  hours  (occasionally  shaking  the  bottle  containing  it 
in  the  interval)  it  ought  to  be  very  opaque  and  creamy. 

The  plate  having  been  coated  with  a substratum,  or 
edged  (see  Chap.  XVI.),  the  collodion,  which  should  have 
been  shaken  about  half  an  hour*  before,  is  poured  on  it 
in  the  ordinary  manner,  and,  when  set,  immersed  in  a dish 
of  distilled  or  rain  water.  When  all  greasiness  has  dis- 
appeared, it  is  flooded  with  any  of  the  preservatives  given 
in  Chap.  XVII.  Canon  Beecliey  recommends  the  plate  to 
be  immersed  in  a dish  containing  beer  to  which  1 grain  per 
ounce  of  pyrogallic  acid  has  been  added.  The  drying  is 
conducted  in  the  usual  manner.  The  exposure  may  be 
taken  to  be  about  twice  that  which  is  necessary  for  a wet 
plate.  Between  exposure  and  development  the  plate  will 
keep  fairly  for  a week,  but  after  that  it  seems  to  lose 
detail,  and  appears  under-exposed. 


* Canon  Beechey  recommends  the  bottle  to  be  shaken  immediately  before 
use,  and  the  emulsion  filtered. 


CHAPTER  X. 


M.  CHARDON’S  PROCESS. 

In  preparing  the  collodion  for  this  process,  M.  Chardon 
prefers  the  use  of  two  kinds  of  pyroxyline,  both  of  which 
have  previously  been  precipitated  from  collodion  into 
water  (see  page  37).  The  one  pyroxyline  is  prepared  in 
the  manner  given  at  page  37  ; the  other,  the  high  tempera- 
ture cotton,  prepared  as  at  page  38.  These  are  mixed  in 
the  solvents  to  form  collodion. 

A salted  collodion  is  made  up  as  follows  : — 

Alcohol  ...  ...  ...  ...  1 ounce 

Ether  ...  ...  ...  ...  2 ounces 

Double  bromide  of  cadmium  and 

ammonium  ...  ...  ...  14  grains 

Zinc  bromide  ...  ...  ...  14  „ 

Precipitated  pyroxyline,  ordinary  7 „ 

Precipitated  pyroxyline,  high 

temperature 28  „ 

A stock  of  this  is  made,  and,  when  settled,  decanted  off 
as  required.  It  must  not  be  filtered,  as  the  evaporation 
of  the  solvents  is  said  to  cause  a change  in  the  sensitive- 
ness of  the  finished  emulsion,  though  we  doubt  it. 

The  collodion  is  rendered  sensitive  in  small  quantities 
at  a time. 


60 


M.  chardon’s  process. 


The  silver  nitrate  is  finely  powdered,  the  quantities 
being  as  follows  : — 

The  above  salted  collodion  ...  1 ounce 

Silver  nitrate  ...  ...  ...  6*2  grains 

Alcohol  •••  •••  ...  3 ounces 

The  ordinary  means  already  described  are  employed  for 
forming  the  emulsion  (see  page  48).  The  emulsion  is 
vigorously  shaken  in  a bottle,  and  put  aside  for  thirty-six 
hours  to  ripen.  After  this  time  has  elapsed,  about  an 
ounce  of  pure  distilled  water  is  placed  in  a glass  beaker, 
and  a drachm  of  the  emulsion  poured  into  it ; after  agi- 
tating the  mixture  it  is  filtered  clear,  which  can  be  effected 
by  passing  it  once  or  twice  through  the  filter  paper. 
This  waste  is  tested  for  silver  nitrate.  A slight  milkiness 
on  the  addition  of  a chloride  is  all  that  is  allowable.  If 
it  shows  no  signs  of  free  silver  nitrate,  more  of  the  latter 
salt  dissolved  in  alcohol  is  added  to  the  emulsion  just  to 
give  the  necessary  milkiness.  This  emulsion  thus  formed 
is  next  corrected  by  a collodion  in  which  cobaltic  chlo- 
ride is  dissolved,  made  as  follows  : — 


Alcohol  ... 

Ether 

Cobaltic  chloride 
Pyroxline 


...  1 

...  H 
...  60 
...  12 


ounce 

ounces 

grains 

5? 


Of  this  he  adds  about  two  drachms  to  each  10  ounces  of 
emulsion;  as  before  stated  in  this  work  (page  10),  all 
causes  of  fog  are  thus  eliminated. 

The  novelty  of  M.  Chardon’s  process  is  now  to  be  ex- 
plained. He  takes  the  finished  emulsion,  and  pours  it 
in  a fine  stream  into  a large  quantity  of  water.  After 
stirring,  the  precipitated  emulsion  is  filtered  through  a 
cloth,  is  washed  carefully  (the  method  indicated  at  page  40 
will  answer),  pressed  between  folds  of  blotting-paper,  and 
dried  in  the  dark.  This  gives  a flocculent  powder  of  a 


M.  CHARDON  S PROCESS. 


()1 


clear  yellow  colour.  To  prepare  the  finished  emulsion 
the  following  is  prepared  : — 

Ether  ...  \ ounce 

Alcohol  ...  .' ...  i „ 

Precipitated  quinine  ...  ...  1 grain 

The  precipitated  quinine  can  be  made  from  the  ordinary 
sulphate  of  quinine  by  dissolving  it  in  sulphuric  acid,  and 
then  adding  ammonia.  The  precipitate  thus  formed  is 
employed. 

The  organic  substance  is  first  dissolved  in  the  alcohol, 
and,  after  filtering,  the  ether  is  added.  To  this  amount 
of  solvents  17  grains  of  the  dried  powder  is  added.  After 
some  hours,  when  all  is  in  solution,  the  emulsion  is  filtered 
through  cotton-wool  (see  Chap.  XYI.)  M.  Chardon  states 
that  the  quinine  gives  porosity  to  the  film  ; but  it  seems 
more  probable  that  it  acts  like  some  other  organic 
matters — viz.,  prevents  a tendency  to  fog. 

The  exposure  for  plates  prepared  by  this  process  is 
stated  to  be  about  double  that  required  for  a wet  plate. 


CHAPTER  XI. 


DAWSON’S  PROCESS. 


The  next  process  which  we  shall  describe  is  one  in 
which  an  11  organifier  ” is  added  to  the  emulsion,  and  leads 
up  to  the  more  complicated  form  recommended  by  Mr. 
Carey  Lea.  We  are  indebted  to  the  British  Journal 
A Imanac  for  the  formulae,  which  are  as  follows  : — 


Collodion . 

Pyroxyline 
Cadmium  bromide 
Ammonium  bromide 
Ether  *725 

Alcohol  *810  


8 grains 


7 

2 


33 

33 


^ ounce 

i 

^ 33 


In  practice  we  have  found  no  difference  in  result,  if  ether 
of  *730  be  used,  and  alcohol  of  *812. 

In  our  experience  we  find  that  the  collodion  should 
be  allowed  to  settle  some  days,  and  then  be  decanted 
off.  The  pyroxyline  employed  may  be  that  given  at 


page  21. 

To  sensitize  this,  a mixture  is  made  of — 


Silver  nitrate  . . . 
Acetic  acid 
Glycerine 
Alcohol  *830 


...  13  grains 

...  2 drops 

1 drachm 
4 drachms 


dawson’s  process. 


63 


These  are  dissolved  in  the  usual  manner,  it  being, 
perhaps,  the  better  plan  to  leave  the  glycerine  out  till  the 
last  minute.  Alter  emulsification  (page  48)  it  is  allowed 
to  stand  twenty-four  hours,  and  then  2 drops  of  hydro- 
chloric acid  are  added  to  the  above  quantities.  It  is 
allo  wed  to  rest  for  another  twenty-four  hours. 

The  emulsion  is  poured  out  into  a dish  of  sufficient 
capacity,  in  order  for  the  solvents  to  evaporate,  and  in  five 
or  six  hours  it  is  ready  for  further  treatment.  This  con- 
sists in  covering  the  pellicular  mass  with  water  for  an  hour, 
and,  after  pouring  off,  covering  it  for  a similar  time  with — 


Tannin 

Gallic  acid 
Acetic  acid 
Water  (distilled)... 


...  5 grains 

...  2 „ 

...  2 drachms 

...  1 ounce 


The  washing  is  now  commenced  in  a manner  similar  to 
that  already  described  at  page  37,  till  ail  traces  of  acid  are 
removed,  which  can  be  tested  by  litmus  paper.  When  all 
the  water  is  wrung  out,  the  emulsion  is  dried  in  a hot  water 
bath,  or  spread  out  in  a warm  room  on  blotting-paper. 

The  mode  of  eliminating  all  traces  of  water  by  alcohol 
is  not  admissible  in  this  case,  as  it  would  dissolve  out  the 
tannic  and  gallic  acid  which  may  be  left  in  the  pellicle. 

To  re-dissolve  the  pellicle,  equal  quantities  of  ether  and 
alcohol  are  used,  having  the  same  specific  gravity  as  that 
given  above.  Dr.  Dawson  recommends  that  it  be  soaked 
in  the  alcohol  for  twelve  hours  before  adding  the  ether. 

The  development  of  the  plates  can  be  carried  out  by 
the  strong  alkaline  development. 


CHAPTER  XII. 


CAREY  LEA’S  CHLOR-IODO-BROMIDE  PROCESS. 


In  tliis  process  we  have  silver  iodide  emulsified  with  bro- 
mide and  chloride,  and,  in  some  hands,  it  works  well.  The 
following  description  will  show  how  the  emulsion  is  pre- 
pared. The  collodion  is  made  thus — 

Ether,  *730  4 drachms 

Alcohol,  *805  4 „ 

Pyroxyline  ...  ...  ...  8 grains. 

The  cotton  may  be  any  of  those  given  in  Chap.  VI.  To 
every  ounce  of  collodion  the  following  are  added : — 

Dried  cadmium  bromide  ...  9 grains 

Ammonium  bromide  ...  2 \ „ 

Ammonium  iodide  ...  ...  2 „ 

Directly  before  emulsifying,  add — 

Aqua  regia  ...  ...  ...  2 drops 

The  emulsion  with  an  excess  of  silver  is  formed  by 
adding  25  to  30  grains  of  silver  nitrate ; and  after  an 
hour’s  interval,  2 grains  of  cupric  chloride  or  cobaltic 


CAREY  LEA’S  CHLOR-IODO-BROMIDE  PROCESS.  65 


chloride  ; 2 drops  of  hydrochloric  acid  may  he  substituted 
for  either  of  these,  or  for  the  aqua-regia. 

The  emulsion  may  at  first  appear  flakey,  but  after  the 
addition  of  the  chloride  it  is  only  necessary  to  shake 
well  and  leave  it  for  twelve  hoars.  On  again  shaking, 
the  emulsion  will  be  found  perfect.  It  may  be  used 
before  drying,  or  after  drying.  In  the  former  case,  any  of 
the  preservatives  ordinarily  used  may  be  employed. 

If  it  has  to  be  dried,  it  is  poured  out  into  a dish  and 
left  till  it  is  in  a leathery  condition  on  the  surface,  after 
which  a preservative  is  poured  upon  it.  Any  preserva- 
tive will  answer,  but  Mr.  Lea  recommends 


Water 

Acetic  acid ... 

Solution  of  gum-arabic  with  sugar 
Prepared  albumen  ... 

Gallic  acid  (60  grains  to  1 ounce 
of  alcohol) 

Tannin  (60  grains  in  1 oz.  of  water) 


6 ounces 

3 drachms 

4 „ 

1 ounce 
4 drachms 


The  albumen  is  prepared  by  the  addition  of  an  equal 
bulk  of  water  to  the  white  of  one  egg,  and  clarifying  with 
12  drops  of  acetic  acid. 

The  gum  and  sugar  solution  is  made  by  mixing  half- 
a-pound  of  gum-arabic  and  two  ounces  of  sugar  in  44 
ounces  of  water,  and  adding  1J  drachms  of  carbolic  acid. 

The  pellicular  mass  is  then  broken  up,  and  it  and  the 
preservative  are  transferred  to  a large  glass  jar  and  left 
there  twenty  minutes.  The  preservative  is  then  poured 
off,  and  the  washing  takes  place  as  given  at  page  52. 

Instead  of  drying  the  emulsion,  it  may  be  poured  direct 
into  the  preservative,  taking  care  that  the  latter  is  more 
than  four  times  the  bulk  of  the  former.  The  washing  in 
this  case  takes  place  by  decantation  in  the  usual  manner. 
This  last  method  is  stated  to  give  the  most  soluble  pellicle. 
The  pellicle  is  then  dried  in  the  oven  or  water  bath,  and 


66  CAREY  lea’s  chlor-iodo-bromide  process. 


isf  re-emulsified  by  taking  for  each  three  ounces  of  the 
original  collodion — 

Ether...  ...  ...  ...  ...  1 ounce 

Alcolol  ...  1 „ 

Plain  collodion  (4  grains  of  pyroxy- 

line  to  the  ounce)...  ...  ...  2 ounces 

Shake  well  at  intervals,  and  in  a week  it  is  ready  for  use. 
The  plate  is  coated  in  the  ordinary  manner,  and  dried. 
The  exposure  is  about  equal  to  that  of  a wet  plate. 


CHAPTER  XIII. 


MR.  H.  COOPER’S  COLLODIO-BROMIDE  RELIABLE 
DRY-PLATE  PROCESS. 

Mr.  Cooper’s  formula  is  as  follows 

u Prepare  first  a stock  of  plain  collodion  by  dissolving 
160  grains  of  ordinary  pyroxyline*  in  six  ounces  absolute 
alcohol  and  ten  ounces  ether.  Good  methylated  alcohol 
will  answer  for  these  first  solvents,  as  also  ether  s.g. 
•730,  purchasable  at  Is.  6d.  per  lb.  Also  make  an  alco- 
holic solution  of  zinc  bromide,  80  grains  to  the  ounce. 
Even  after  filtering,  this  solution  will  throw  down  a 
deposit  upon  keeping,  and  this  must  be  carefully  left  un- 
disturbed. To  make  10  ounces  of  washed  emulsion,  take 
5 ounces  of  the  above  collodion,  and  add  to  it  one  ounce 
of  the  zinc  bromide  solution,  and  20  minims  of  syrupy 
lactate  of  ammonia. t Sensitize  with  150  grains  of  silver 
nitrate,  dissolved  first  in  80  minims  of  water,  and  then  in 
3 ounces  strong  alcohol.  Boil  together,  and  add  it  to  the 
bromised  collodion  at  once.  I attach  importance  to  the 


* Mr.  Cooper  recommends  the  pyroxyline  as  prepared  by  Hopkin  and 
Williams,  as  answering  the  purpose. 

t “ Small  experiments  made  since  this  paper  was  first  written  go  to  show 
that  a great  gain  in  sensitiveness  may  be  obtained  by  reducing  the  propor- 
tion of  plain  collodion.  I have  tried  three  ounces,  and  even  two  ounces, 
instead  of  the  five,  with  the  most  encouraging  results.  I am  indebted  to 
a leader  in  the  British  Journal  for  the  suggestion.” 


68 


cooper’s  collodio-bromide  process. 


addition  of  the  boiling  solution,  so  as  to  raise  the  tempera- 
ture of  the  mixture,  and  when  only  a small  quantity  (such 
as  the  above)  is  made,  I take  the  precaution  to  wrap  the 
bottle  in  a thick  cloth  to  retain  the  heat  as  long  as 
possible.  On  examining  the  portions  just  given,  it  will  be 
seen  that  the  silver  nitrate  is  decidedly  in  excess,  and  that 
the  alcohol  is  used  in  larger  proportion  than  usual. 

u Lactate  of  silver  has  long  been  a favourite  addition  of 
mine  to  emulsions,  and  I am  more  than  ever  pleased 
with  its  action.  I must  call  attention  to  a curious  effect 
which  is  produced  if  the  bromised  collodion  is  allowed 
to  stand  many  minutes  after  the  lactate  is  added,  and 
before  the  sensitizing.  The  collodion  becomes  quite 
milky,  and  throws  down  a crystalline  deposit.  It  is  well 
to  add  the  lactate  immediately  before  the  silver,  or  even 
to  defer  putting  it  in  until  after  the  sensitizing.  I cannot 
pretend  to  say  what  chemical  or  physical  effect  occurs  in 
the  : lactised  ’ collodion  : I merely  mention  the  fact. 

u The  emulsion  is  ripe  in  about  twenty-four  hours  ; but 
I am  disposed  to  think  it  an  improvement  to  keep  it  for 
a longer  time,  up  to  three  days.  At  the  expiration  of  the 
ripening  period,  twenty  minims  of  strongest  nitric  acid 
are  to  be  added,  and  the  emulsion  well  shaken.  I prefer 
to  add  the  acid  just  before  the  Trashing  instead  of  at 
first.  I believe  a better  film  is  given  by  so  doing. 

a We  are  now  faced  with  the  question  of  how  best  to 
wash  the  emulsion.  Shall  we  pour  it  out  and  evaporate 
the  solvents,  or  precipitate  it?  From  a lengthened 
experience  of  both  methods,  I cannot  recommend  pre- 
cipitation, except  in  cases  where  the  finished  emulsion  is 
to  be  used  up  within  a month.  It  is  now  a generally 
acknowledged  fact  that  precipitated  emulsions  will  not 
keep  well.  But  where  large  batches  of  plates  can  be 
prepared  at  a time,  and  no  waste  occurs,  I can  speak 
to  the  good  qualities  of  the  emulsion  when  precipitated 
by  mixing  it  with  twice  its  bulk  of  the  following  organi- 
fier,  and  when  the  pellicle  has  fully  separated  and  set, 


cooper’s  collodio-bromide  process. 


69 


washing  for  some  time  in  water  containing  a little  nitric 
acid  (half-ounce  to  one  gallon),  and  finally  in  several 
changes  of  pure  water.  The  mixture — 


Tannin  ... 

Gallic  acid 
Grape  sugar 
Strong  acetic  acid 


500  grains 
200  „ 
200  „ 

10  ounces 


or  a proportionately  lesser  quantity  of  glacial,  to  he 
dissolved  in  water,  and  make  up  to  100  ounces.  This 
method  is  expeditious.  The  alternative,  and  I think 
the  better  plan,  is  to  pour  out  the  emulsion  into  a 
sufficiently  large  dish  (1  ounce  to  25  square  inches,  or 
say  5 ounces  in  a 12  by  10  dish).  Evaporate  the  solvents 
more  thoroughly  than  usual ; in  fact,  the  pellicle  may  be 
allowed  to  get  almost  dry.  Wash  first  in  water  contain- 
ing half-an-ounce  of  nitric  acid  in  one  gallon  of  water,  and 
then  in  plain  clean  water  for  some  considerable  time.  If 
the  water  in  use  is  hard,  distilled  water  should  be  used  at 
first  and  lastly.  Wash  thoroughly.  The  extra  drying  of 
the  pellicle  and  the  large  proportion  of  alcohol  it  con- 
tained will  materially  assist  in  shortening  the  time. 
When  dry,  dissolve  the  above  quantity  of  pellicle  in 
5 ounces  of  pure  absolute  alcohol,  and  a like  quantity 
of  extra  purified  methylated  ether,  s.g.  *720.  An  emulsion 
prepared  in  this  manner  with  the  lactate  of  ammonia  will 
give  excellent  negatives  without  further  preparation  if 
the  plates  are  used  at  once ; but  its  subsequent  treatment 
with  alkaline  albumen  gives  the  especial  qualities  for 
which  I had  so  greatly  valued  it.  The  plates  are  much 
quickened  by  the  after  treatment.  This  particular  emul- 
sion has  its  sensitiveness  doubled,  whilst  some  others  are 
rendered  slower.” 

Mr.  Cooper  then  describes  gelatinizing  the  plates  with 
gelatine  and  chrome  alum  as  given  at  page  77.  He  says 
that  small  plates  may  have  an  edging  only  (page  75),  but 
that  he  prefers  giving  them  the  full  coating  : — 


70  cooper’s  collodio-bromide  process. 

“ Coat  with  the  emulsion.  When  well  set,  immerse  in 
water.  I myself  use  a grooved  box,  well  coated  with 
shellac,  and  when  I have  coated  and  immersed  as  many 
plates  as  I intend  to  prepare,  I cover  up  the  box  and 
thoroughly  ventilate  the  room,  so  as  to  get  rid  of  all 
fumes  of  alcohol  and  ether  before  proceeding  further.  I 
see  no  reason  why  a tin  box  with  removable  grooved 
pieces,  similar  to  the  one  sent  out  by  the  Autotype 
Company  for  developing  chromotypes,  should  not  answer. 
Of  course  it  must  be  kept  for  the  purpose  alone. 

“ The  plates  are  now  to  be  flooded  with  the  alkaline 
albumen,  or  dipped  in  a bath  of  it.  In  either  case  the 
albumen  must  be  in  contact  with  the  film  for  at  least  a 
minute.  The  plate  is  then  to  be  thoroughly  washed, 
flowed  with  a preservative,  drained,  and  dried.  After 
backing  it  is  ready  for  the  camera.  The  albumen  may 
be  prepared  in  bulk,  either  with  whites  of  eggs,  or  with 
the  pure  dried  preparation.  Of  the  latter,  dissolve  60  grs. 
in  3 ounces  of  water,  and  add  1 drachm  of  strongest 
liquor  ammonia  *880.  If  white  of  egg  be  used,  first  pour 
in  a few  minims  of  dilute  acetic  acid,  and  well  stir.  In 
two  or  three  hours  strain,  and  to  each  ounce  add  two  of 
water  and  one  drachm  of  liquor  ammonia. 

“For  the  1 preservative  ’ I have  tried  a host  of  sub- 
stances, and  find  the  simplest  of  all  to  be  the  best — 
viz.,  a two-grain  solution  of  gallic  acid.  For  the  sake  of 
constant  uniformity  and  certainty,  I was  anxious  to  dis- 
card from  my  formulae  all  compounds  of  uncertain 
chemical  constitution,  such  as  beer,  or  even  tea  and  coffee, 
or  else  I could,  from  my  own  experience,  speak  strongly 
in  favour  of  a decoction  of  tea,  made  by  boiling  1 ounce 
of  compressed  black  tea  in  4 ounces  alcohol  and  12  ounces 
water.  One  ounce  of  this  is  diluted  with  10  ounces  of 
water  to  form  the  final  coating  for  the  plate.  It  is  of 
importance  that  the  plates  should  be  thoroughly  dried, 
especially  if  intended  for  packing ; as  although  these  plates 
will  stand  exposure  to  a moist  atmosphere  better  than 


cooper’s  collodio-bromide  process. 


71 


most  others,  any  damp  remaining  in  the  films  when  they 
are  stored  away  will  be  a source  of  future  trouble.” 

Mr.  Cooper  recommends  a full  exposure  in  the  camera 

f 

for  these  plates.  We  have  found  that  with  a stop  and 

in  an  open  landscape  and  good  light,  thirty  seconds  are 
ample;  but  that  three  minutes  may  be  given  without 
detriment.  Of  the  negatives  produced  by  this  process, 
Mr.  Cooper  says  : — 

u First,  the  quality  of  image  is  almost  perfect,  much 
resembling  that  given  by  a really  good  collodio- 
albumen  plate.  Secondly,  the  films  will  keep  for  a lengthy 
period  without  deterioration,  both  before  and  after 
exposure.  I exhibit  a negative  which  was  kept  five 
months  before  exposure,  remaining  for  three  months 
in  a dark  slide,  and  carried  about  on  long  journeys,  being 
submitted  to  many  variations  of  temperature  and  hygro- 
scopic conditions  of  the  atmosphere.  After  exposure  and 
before  development  it  was  kept  five  weeks.  Other  plates 
have  been  kept  three  months  after  exposure.  I give  these 
data,  as  many  folks’  ideas  of  a 1 lengthy  period  ’ are 
various.  I have  plates  prepared  early  this  year  which  I 
am  keeping  on  to  test  from  time  to  time. 

u In  exposure,  very  great  latitude  is  allowable — an 
unspeakable  boon  to  the  photographer  on  a tour,  with  no 
conveniences  for  developing  a trial  plate  from  time  to 
time.” 


CHAPTER  XIY. 


COLLODIO— BROMIDE  EMULSION  WITH  EXCESS 
OF  BROMIDE. 


The  writer,  in  some  recent  investigations,  was  led  to 
the  conclusion  that,  theroretically,  the  loss  of  sensitiveness 
due  to  using  a collodio-bromide  emulsion  with  an  excess 
of  soluble  bromide  must  be  due  to  the  want  of  a bromine 
absorbent ; and  that  if,  with  an  excess  of  soluble  bromide, 
we  had  the  presence  of  such  an  absorbent,  that  then  the 
sensitiveness  should  be  in  a great  measure  restored. 
When  light  causes  the  liberation  of  bromine  from  the 
silver  bromide  (see  page  9),  and  when  a bromine  absor- 
bent, such  as  potassium  nitrite,  is  present,  we  have  the 
following  reaction : — 

-a  Potassium  Wo  _•  Hydrobromic  Potassium 

Bromide  and  Nitrite  and  Water  give  Acid  and  Nitrate 

2Br  + KN02  + HoO  = 2HBr  -f  KNO3 


The  hydrobromic  acid  liberated  would  have  a tendency 
to  destroy  the  image  ; hence  it  is  desirable  that  a neutral 
compound  should  be  formed.  This  will  be  the  case  if  an 
alkaline  carbonate  be  added,  for  then  we  have — 


Potassium 

Bromine  Nitrite  and 

2Br  + KNO2 


Sodium  • 
Carbonate  g Te 
JL  Na  > CO,  — 


Sodium  Potassium  •, 
Bromide  Nitrate  ana 

2NaBr  + KN03  + 


Carbonic 

Anhydride 

CO2 


This  practically  was  proved  to  be  the  case.  In  making 
a washed  emulsion  with  excess  of  bromide,  it  will  be 


COLLODIO-BROMIDE  EMULSION. 


73 


well,  then,  to  add  to  every  ten  ounces  of  emulsion  two 
drachms  of  a saturated  solution  of  potassium  nitrite  in 
alcohol,  and  to  apply  to  the  film  sodium  carbonate  in  the 
first  wash  water,  and  then  to  wash  again.  By  this  means 
the  retarding  effect  of  any  trace  of  soluble  bromide  left  is 
counteracted  by  the  presence  of  the  trace  of  potassium 
nitrite  and  of  sodium  carbonate. 

The  following  formulae  will  be  found  to  form  a very 
excellent  emulsion,  giving  very  beautiful  films,  which,  for 
sensitiveness,  are  not  behind  those  which  are  prepared 
with  excess  of  silver  nitrate.  It  is  based  on  the  alteration 
which  is  caused  in  the  molecular  structure  of  silver  bro- 
mide by  the  use  of  ammonia,  as  adopted  for  the  gelatine 
process. 

The  ordinary  collodion  is  formed  as  follows 

Pyroxyline  (high  temperature)  25  grains 
Alcohol 2 ounces 


To  this  is  added  100  grains  of  zinc  bromide. 

In  order  to  emulsify  this,  100  grains  of  silver  nitrate 
are  dissolved  in  the  smallest  possible  quantity  of  water, 
made  up  to  1 ounce  with  alcohol,  s.g.  about  *820,  and 
liquor  ammonia  added,  drop  by  drop,  till  the  oxide  first 
precipitated  is  re-dissolved.  The  emulsion  is  then  formed 
as  given  at  page  49.  It  is  immediately  placed  in  a dish 
to  evaporate  (see  page  50),  when  it  is  at  once  washed  till 
it  shows  no  alkaline,  or  a very  faint  trace  of  alkaline, 
reaction.  The  water  may  be  eliminated  by  the  alcohol 
plan,  or  by  drying,  as  given  at  page  52. 

The  pellicle  is  then  dissolved  in  2%  ounces  of  alcohol  and 
2J  ounces  of  ether.  It  will  be  noticed  that  the  proportion 
of  pyroxyline  to  silver  bromide  is  too  small.  Plain  collo- 
dion made  as  follows  should  therefore  be  judiciously 
added,  till  a silver  of  good  quality  is  obtained : — 

Pyroxyline  ordinary  ...  ...  50  grains 


Ether 


Ether  *720 
Alcohol  -805 


5 ounces 
5 


3? 


74 


COLLODIO-BROMIDE  EMULSION. 


This  must  be  added  judiciously.  It  will  probably  be 
found  that  as  much  as  5 ounces  of  this  will  have  to  be 
added ; but  a good  deal  depends  on  the  quality  of  the 
pyroxyline. 

The  emulsion  should  be  orange  when  mixed,  and  also 
after  washing.  It  should  be  powdery  to  the  touch  when 
a plate  is  coated  with  it.  It  will  be  found  to  be  as  rapid 
as  a wet  plate,  and  if  a preservative  be  used  (see  Chap. 
XVII.)  which  will  stand  the  employment  of  undiluted 
ferrous  oxalate,  it  will  be  found,  if  rightly  prepared,  a good 
deal  more  sensitive.  The  development  takes  place  by  the 
alkaline  method  if  preferred.  An  emulsion  may  be  made 
by  the  same  formula  as  above,  omitting  the  ammonia.  It 
will  be  found  slower. 


CHAPTER  XV. 


COLLODIO- ALBUMEN  EMULSION. 

The  writer  introduced  to  the  photographic  public  an 
emulsion  made  with  albumen,  which  proved  to  be  very 
sensitive,  and  some  skilled  photographers  were  pleased 
with  it.  The  process  is  given  here,  as  it  may,  perhaps, 
be  used  as  a starting  point  from  which  other  emulsions 
may  be  satisfactorily  deduced.  In  the  hands  of  the  writer 
the  images  were  inclined  to  be  thin,  but  when  chloride  is 
introduced  it  is  found  that  this  lack  of  density  vanishes  to 
a great  extent,  and  leaves  a very  delicate  and  printable 
image.  The  following  is  the  mode  of  preparation: — 16 
grains  of  ordinary  cotton  are  dissolved  in  6 drachms  of 
ether  (*730)  and  4 of  alcohol  (*805),  and  the  plain  collodion 
thus  formed  decanted.  20  grains  of  zinc  bromide  are 
dissolved  in  a small  quantity  of  alcohol,  and  enough  bro- 
mine water  added  to  tinge  the  solution  with  a very  pale 
yellow.  This  is  added  to  the  above  amount  of  plain  collo- 
dion. F or  each  half  ounce  of  the  above,  1 grain  of  dried 
albumen  is  taken  and  dissolved  in  the  least  possible 
quantity  of  water,  or  8 drops  of  the  white  of  an  egg 
may  be  dropped  into  a drachm  of  alcohol,  and  thoroughly 
stirred.  Either  of  these  solutions  is  then  carefully 
dropped  into  the  collodion  (placed  as  usual  in  a jar),  and 
well  stirred  up.  This  should  form  an  emulsion  of  albumen 
in  the  collodion.  F orty  grains  of  silver  nitrate  are  next 
added  in  the  way  pointed  out  on  page  33,  after  having 


76 


COLLODIO-ALBUMEN  EMULSION. 


been  dissolved  in  the  smallest  possible  quantity  of  water 
and  boiling  alcohol.  A beautifully  smooth  emulsion 
should  result  from  this.  Mr.  Berkeley,  who  has  tried  this 
emulsion,  proceeds  in  a slightly  different  way  : he  adds  the 
cotton  to  the  ether,  then  adds  the  albumen,  and  finally 
adds  the  amount  of  zinc  bromide  in  the  necessary  amount 
of  alcohol. 

The  amount  of  silver  nitrate  added  ensures  that  there  is 
an  excess  of  at  least  two  grains  in  each  ounce  of  the 
emulsion 

Instead  of  the  emulsion  being  made  entirely  with  zinc 
bromide,  greater  density  may  be  obtained  by  omitting  four 
grains  of  it,  and  adding  four  grains  of  calcium  chloride. 

The  emulsion  is  next  poured  out  into  a dish,  and  the 
ordinary  manipulation  carried  out.  After  a couple  of 
washings  it  may,  however,  advantageously  be  covered 
with  a weak  solution  of  silver  nitrate,  and  again  washed 
till  the  traces  of  silver  are  very  faint. 

The  pellicle  should  be  re-dissolved  in  equal  quantities  of 
ether  and  alcohol,  and  finally  there  should  be  about  seven 
grains  of  the  pyroxyline,  as  originally  used,  to  each  ounce 
of  the  mixed  solvents. 

The  emulsion,  when  finished,  generally  gives  a tender 
blue  by  transmitted  light,  and  is  seemingly  transparent. 
It  may  have  a tendency  to  curl  off  the  plate  on  drying, 
in  which  case  the  addition  of  a little  ordinary  washed 
emulsion  will  correct  it.  It  will  develop  with  plain  pyro- 
gallic  acid,  and  can  be  intensified  by  pyrogallic  and  citric 
acid,  with  the  addition  of  a tew  drops  of  silver  nitrate  solu- 
tion, or  it  can  be  developed  by  the  alkaline  developer,  or 
the  ferrous  oxalate  developer  (page  51),  or  the  hydro- 
sulphite developer  (page  54).  Some  photographers  have 
found  a tendency  in  it  to  form  blisters  when  developing. 
This  has  not  happened  to  the  writer  when  the  developer 
was  kept  above  60°  F.  In  some  hands  this  emulsion  is 
extremely  rapid — so  much  so,  as  to  require  very  con- 
siderably less  exposure  than  an  ordinary  wet  plate. 


CHAPTEK  XVI. 


PREPARATION  OF  THE  PLATE 

When  we  require  a glass  plate  to  use  without  a substra- 
tum, we  usually  soak  the  plates  in  nitric  acid  and  water, 
and  then  wash  under  the  tap,  and  carefully  dry  with  a 
cloth ; a cream  of  tripoli  powder  in  alcohol  is  then  rubbed 
over  the  plate,  and  allowed  to  dry.  When  a plate  is 
required  for  use,  the  tripoli  is  rubbed  off  with  a soft 
cloth,  and  it  is  left  unpolished  ; a small  piece  of  blotting- 
paper  is  then  folded  up  in  the  shape  of  a small  spill,  and 
dipped  in  a solution  of  albumen  in  water  (the  strength  is 
immaterial),  and  the  plate  is  given  an  edging  by  placing 
the  moistened  end  of  the  spill  beneath  the  thumb  of  the 
right  hand,  and  drawing  it  round  the  edge  of  the  plate. 
By  this  means  a u safe  edge  ” is  given  to  it.  The  amount 
of  fluid  required  is  so  small  that  the  first  edge  may  be 
dry  before  the  last  is  finished,  and  yet  sufficient  for  the 
purpose  will  be  on  the  plate. 

Some  persons  rub  French  chalk  or  talc  over  the  surface 
of  the  plate,  and  this  will  be  found  effective  when  using 
washed  emulsion,  without  giving  an  edging  ; but  we 
honestly  confess  that  where  a preservative  is  used,  this 
is  hardly  sufficient.  In  our  own  experience  a film  will 
adhere  to  the  surface  when  it  is  only  once  wetted  with 
water,  but  not  twice.  In  this  case  a substratum  must  be 


78 


PREPARATION  OF  THE  PLATE. 


employed  to  cause  the  necessary  adhesion  of  the  film  to 
the  plate.  The  following  answers  : — 


Sheet  gelatine 
Distilled  water 
Ammonia 
Alcohol 


...  75  grains 

...  60  ounces 

£ ounce 


The  gelatine  should  he  first  softened  in  half  the  quantity 
of  water,  and  the  remainder  added  in  the  boiling  state, 
which  will  dissolve  it ; when  cool  the  ammonia  and  alcohol 
should  be  added,  and  it  should  be  carefully  filtered. 

The  late  Mr.  Henry  Cooper  introduced  a new  gelatine 
substratum,  the  preparation  and  application  of  which  he 
describes  as  follows  : — 

u Soak  60  grains  of  Nelson’s  photographic  gelatine 
in  water,  drain,  and  pour  on  enough  boiling  water  to  make 
8 fluid  ounces.  Now  add  2 drachms  of  a ten-grain 
solution  of  chrome  alum,  and  stir  vigorously  for  a minute 
or  two.  Filter  the  solution  through  paper  into  a clean 
measure,  keeping  it  warm  and  avoiding  air-bubbles. 

u To  save  trouble,  a large  quantity  of  each  of  the  solu- 
tions, the  gelatine  and  the  chrome  alum,  may  be  prepared, 
and  will  keep  for  a long  time  if  a little  pure  carbolic  acid 
be  added  to  each.  No  more  must  be  mixed  than  is  re- 
quired for  the  batch  of  plates,  as  when  the  compound 
solution  has  once  become  cold,  it  cannot  be  again  liquefied 
with  heat.  The  measure  and  filter  used  must  be  well 
washed  with  warm  water  as  soon  as  done  with,  for  the 
same  reason.” 

Albumen  may  also  be  used. 

White  of  egg  ...  ...  ...  1 ounce 

Water  ...  ...  ...  ...  100  ounces 

Ammonia  ...  ...  ...  ...  5 drops 

50  grains  of  dried  albumen  may  be  substituted  for  the  white 
of  egg.  The  albumen  and  water  should  be  well  shaken 
together  in  a bottle  for  five  minutes,  and  then  be  filtered 
through  fine  filter-paper,  taking  care  to  avoid  air-bubbles. 


PREPARATION  OF  THE  PLATE. 


79 


A better  formula,  however,  seems  to  be  one  due  to  Mr. 
Ackland,  and  is  thus  described  by  Mr.  W.  Brooks  : — 

The  whites  of  fresh  eggs  are  collected,  and  to  every 
8 ounces,  one  ounce  of  water  and  24  drops  of  glacial 
acetic  acid  are  added,  by  pouring  it  into  the  albumen 
in  a fine  stream,  and  stirring  evenly  with  a glass  rod 
for  one  or  two  minutes.  The  albumen  should  on  no 
account  be  beaten  or  whisked  up,  or  the  resulting  prepara- 
tion will  be  milky.  It  is  allowed  to  rest  one  hour  or  more, 
and  is  then  strained  through  coarse  muslin  or  cheese  cloth. 
To  the  strained  albumen  is  added  one  drachm  of  the 
strongest  liquid  ammonia  (*880),  when  it  can  be  put  away 
in  corked  bottles  and  kept  for  use. 

To  make  a substratum  Mr.  Brooks  takes — 

Prepared  stock  albumen  ...  1 ounce 

Water  ...  ..  ...  ...  1 pint 

This  is  applied  as  above. 

The  latest  substratum,  and  which  is  due  to  Dr.  Vogel, 
is  as  follows : — Place  (say)  50  grains  of  gelatine  in  a 
flask,  and  add  to  them  about  2 ounces  of  acetic  acid  (it 
is  not  necessary  for  it  to  be  glacial) ; warm  in  boiling 
water  to  dissolve  the  gelatine.  This  amount  of  acetic 
acid  may  not  be  enough  ; if  so,  add  more.  It  is  not  very 
particular  how  much  you  add,  so  long  as  it  is  sufficient. 
When  dissolved,  make  up  to  about  5 ounces  with  ordin- 
ary methylated  spirit.  At  first  the  solution  remains 
opalescent 1 while  the  alcohol  is  added,  but  at  a well- 
marked  point  it  becomes  white,  due  to  the  precipitation 
of  the  gelatine.  No  more  spirit  must  be  added  at  this 
stage,  but  more  acetic  acid  must  be  dropped  in  till  the 
white  curdy  appearance  is  lost.  The  liquid  should  be 
heated  to  aid  the  re-solution.  A grain  of  chrome  alum 
dissolved  in  1 dr.  of  water  must  next  be  added.  You 
then  have  a fluid  which,  when  poured  upon  a glass  plate, 
gives  a most  excellent  substratum.  To  use  it,  filter 
through  paper,  and  coat  the  plate  as  with  collodion; 


80 


PREPARATION  OF  THE  PLATE. 


return  the  excess  into  the  filter,  rock  the  plate  to  do  away 
with  many  lines,  and  dry  over  a Bunsen  burner,  or  a 
spirit  lamp,  or  before  a fire.  The  alcohol  will  rapidly 
evaporate,  and  then  the  acetic  acid  is  driven  off,  and  a 
glassy,  hard  substratum  remains  on  the  surface  of  the 
plate.  Dr.  Vogel  directed  the  plates  to  be  dried  sponta- 
neously; but  if  so,  half  the  valuable  qualities  of  the 
substratum  will  be  lost.  The  rapid  drying  prevents  any 
spots  due  to  dust  falling  on  the  plate  whilst  moist. 

The  cleaning  of  the  plate  is  of  much  greater  importance 
when  a substratum  is  used,  than  where  it  is  omitted, 
the  great  difficulty  being  to  get  an  even  film  on  the 
surface.  It  is  impossible  to  get  this  if  there  be  the  least 
repellent  action  between  it  and  water.  What  the  writer 
recommends  is,  that  the  plates  be  soaked  in  nitric  acid, 
and  be  well  rubbed  with  it  by  means  of  a pad  of  cotton 
wool  ( freed  from  all  resinous  matter  by  previous  soaking  in 
a strong  alkaline  carbonate , and  then  thoroughly  washed  and 
dried),  and  when  the  acid  is  washed  away  under  the  tap, 
that  it  be  followed  by  a solution  of  potash  20  grains, 
alcohol  £ ounce,  and  water  £ ounce,  also  rubbed  in  with 
a pad  of  wool.  When  water  flows  evenly  over  the  sur- 
face, the  plate  should  be  rinsed  in  distilled  water,  and, 
after  a short  draining,  the  gelatine  (except  Dr.  Vogel’s, 
see  above)  or  albumen  solution  should  be  flowed  over 
it,  and  drained  off  immediately.  A very  thin  sub- 
stratum will  thus  be  given,  which  will  dry  rapidly,  and 
be  adherent  to  every  part  of  the  surface.  Another  plan  is 
to  use  the  Blanchard  brush.  A brush  is  made  of  swan’s- 
down  calico,  as  follows  : — A strip  of  glass,  about  six 
inches  long  by  two  broad,  should  be  procured,  and  round 
one  end  should  be  attached,  by  thread  or  india-rubber 
band,  a double  told  of  swan’s-down  calico.  This  brush 
should  be  dipped  in  the  albumen,  and  the  excess  squeezed 
out  against  the  beaker.  The  plate,  which  should  be  dry, 
should  then  be  brushed  smoothly  down  the  surface  in 
parallel  lines  to  within  one-eighth  of  an  inch  of  its  edges, 


PREPARATION  OF  THE  PLATE. 


81 


set  up  to  dry  on  blotting-paper,  and  protected  from  dust. 
When  dried  (which  should  be  done  spontaneously),  the 
plate  will  be  ready  for  the  collodion. 


Some  photographers  recommend  the  use  of  india-rubber 
for  the  substratum. 


India-rubber 

...  1 grain 

Chloroform 

...  1 ounce 

Or, 

India-rubber 

1 grain 

Benzole  ... 

...  1 ounce 

These  are  flowed  over  the  plate  like  collodion,  the  plate,  of 
course,  being  dry.  Unless  the  solutions  be  very  clear,  and 
free  from  all  residue,  a negative  taken  on  a plate  so  coated 
is  apt  to  show  markings.  There  are,  however,  some 
emulsions  which  seem  to  be  totally  independent  of  the 
character  of  a substratum,  and  will  not  show  these  mark- 
ings, even  when  the  india-rubber  solution  is  not  bright. 

Coating  the  Plate. — When  plates  are  to  be  coated,  the 
emulsion  should  be  well  shaken  for  three  or  four  minutes, 
and  be  then  allowed  to  subside  for  ten  minutes.  The  top 
portion  should  then  be  filtered  through  cotton-wool, 
boiled  in  soda,  and  then  thoroughly  washed.  The 
cotton-wool  should  be  placed  in  the  neck  of  a funnel,  and 


82 


PREPARATION  OF  THE  PLATE. 


not  be  too  tightly  pressed  down ; and  a little  strong 
alcohol  passed  through  it  to  moisten  it.  The  first  lot  of 
emulsion  passing  through  the  funnel  should  be  returned  to 
the  bottle,  and  filtered  again.  The  amount  of  emulsion  re- 
quired varies  with  the  number  and  size  of  the  plates  used. 
A trial  plate  is  first  coated  to  see  if  the  emulsion  flows 
readily.  If  it  appears  to  u drag  ” over  the  surface,  it 
should  be  diluted  with  a little  ether  and  alcohol  (2  parts 
of  the  former  to  1 of  the  latter).  It  will  be  found  that 
in  coating  a large  plate  the  emulsion  should  be  thinner 
than  for  a small  plate.  When  it  appears  satisfactory,  the 
emulsion  should  once  more  be  passed  through  the  filter. 
Coating  the  plates  is  next  taken  in  hand.  The  filtered 
emulsion  is  poured  over  the  plate  in  the  usual  manner,  and 
the  plate  tilted  up,  and  rocked  to  and  fro  till  the  ridges  and 
furrows,  so  often  visible  in  these  plates,  have  disappeared. 
The  surplus  collodion  should  be  returned  through  the  filter 
into  another  bottle,  as  by  so  doing  a fresh  portion  of  the 
emulsion  is  used  for  each  plate  coated,  and  there  will  be 
a consequent  freedom  from  specks  due  to  any  dust  which 
may  have  fallen  on  a plate  previously  coated.  If  this  be  a 
washed  emulsion,  it  should  now  be  dried  or  treated  with  a 
preservative  (see  Chap.  XVII.)  If  it  is  to  be  dried,  there 
is  nothing  so  convenient  as  a hot  air  bath,  such  as  used  by 
chemists  in  their  laboratory.  They  can  be  obtained  up  to 
a size  which  will  take  8^  by  6J  plates.  It  is  a good  pre- 
caution to  line  the  inside  with  varnished  paper,  to  prevent 
the  remote  chance  of  any  metallic  specks  depositing  on  the 
plate  during  drying.  If  this  be  not  at  hand,  the  small  piece 
of  apparatus  recommended  by  Woodbury  is  very  effective. 
It  consists  of  an  iron  tripod  stand,  such  as  used  in  the  labo- 
ratories, a flat  sheet  of  cast  iron,*  and  a spirit  lamp  when 
gas  is  not  available.  The  iron  plate  is  placed  on  the  iron 
tripod,  and  the  spirit  lamp  beneath  it.  It  is  advisable  to 


* An  old  pikelet  iron,  in  one  instance  we  are  aware  of,  has  been  success- 
fully employed. 


PREPARATION  OF  THE  PLATE. 


83 


place  a couple  of  pieces  of  blotting-paper  beneath  the 
plate  which  is  to  be  dried.  By  using  the  blotting-paper 
the  plate  will  be  dried  and  heated  uniformly  throughout, 
which  is  not  the  case  when  it  is  placed  directly  on  the  cast 
iron  plate,  for  curvature  in  either  will  prevent  the  two  sur- 
faces coming  in  contact.  The  heat  should  be  so  great  that 
to  touch  the  surface  of  the  blotting-paper  is  unpleasant  to 
the  fingers,  and  the  glass  should  be  allowed  to  assume  the 
same  temperature.  It  may  be  laid  down  as  a maxim  that 
the  more  rapid  the  drying,  the  greater  freedom  there  will 
be  from  all  spots. 

Where  a preservative  is  to  be  employed  with  a leashed 
emulsion , the  plate  must  be  washed  with  water  till  all 
greasiness  disappears,  when  it  may  be  applied  at  once.  If 
an  ( unwashed  emulsion  be  used,  the  plate  must  be  well 
washed  in  distilled  water,  till  all  excess  of  haloid  salt,  if 
that  be  in  excess — or,  as  a rule , of  the  silver  nitrate,  if  that 
be  in  excess — be  thoroughly  eliminated.  The  preserva- 
tive may  then  be  applied  by  flooding  the  film  with  it,  or  by 
immersing  the  plate  in  a flat  dish  or  dipping  bath  con- 
taining it.  The  plates  are  in  this  case  usually  allowed 
to  dry  spontaneously,  but  they  are  generally  improved 
by  a final  dry  over  the  iron  plate  as  directed  above. 

In  Chapter  XVII.  will  be  found  a description  of  pre- 
servatives which  may  be  applied  to  washed  emulsion  with 
success. 

As  the  result  of  very  numerous  experiments,  the  writer 
has  unwillingly  come  to  the  conclusion  that  a washed  emul- 
sion without  a preservative  of  some  kind  is  a dangerous 
process  in  which  to  place  absolute  trust.  Films  which 
would  give  perfect  negatives,  free  from  those  spots  which 
refuse  to  develop,  may,  after  keeping  some  time,  show 
them  in  perfection,  spoiling  every  picture  taken  upon 
them.  An  interesting  experiment  is  to  take  a plate  freshly 
prepared,  and  expose  half  of  it  to  sunlight  to  darken  it, 
and,  after  the  lapse  of  a fortnight,  to  expose  the  other  half. 
Though  the  first  part  may  show  a perfectly  uniform 


84 


PREPARATION  OF  THE  PLATE. 


darkening  of  the  surface,  the  other  half  will,  in  all  proba- 
bility, show  the  spots  by  their  refusal  to  darken  in  certain 
places.  A plate  used  with  a preservative,  on  the  other 
hand,  will  blacken  equally  after  any  length  of  keeping. 
The  cause  of  these  spots  is  rather  obscure,  but  we  think 
we  have  traced  them  to  a quite  unsuspected  cause,  which, 
if  it  prove  correct,  will  indicate  another  use  of  the  preserva- 
tive. It  must  be  remembered  that  the  ordinary  washed 
emulsion  will  be  free  from  the  objection  if  the  plates  are 
prepared  one  day,  and  exposed  and  developed  within  three 
or  four  days.  This  lapse  of  time  is  often  sufficient  for  the 
amateur. 

Backing  the  Plate. — With  some  kinds  of  emulsion,  more 
particularly  if  a gum  or  albumen  preservative  be  used, 
the  films  are  very  translucent,  and  the  image  is  subject 
to  the  well-known  blurring  due  to  light  scattered  by  the 
silver  compound,  and  reflected  from  the  back  of  the  plate. 
This  defect  is  in  a measure  cured  by  applying  some  non- 
actinic  varnish  to  the  back  of  the  plate.  This  backing 
may  be  made  as  follows  : — 


Powdered  burnt  sienna  ... 

Gum  

Glycerine... 

Water 


...  1 ounce 

...  i „ 

...  2 drachms 

...  10  ounces 


The  solution  can  be  brushed  on  with  a hog’s  bristle 
brush.  Ordinary  printers’  .paper  coated  with  gum-arabic, 
stained  with  aurine  or  a blue  absorbent  dye,  and  fastened 
on  the  plate,  is  as  clean  a method  of  backing  a plate  as 
can  be  desired.  Whichever  backing  is  employed,  it 
should  be  removed  previous  to  the  development  of  the 
plate,  and  it  is  often  convenient  to  do  so  after  the  alcohol 
has  been  applied  to  the  surface  of  the  film,  and  before 
washing  with  water.  The  alcohol  repels  any  water 
containing  the  soluble  part  of  the  backing,  and  thus  pre- 
vents staining  of  the  image.  A small  tuft  of  cotton-wool 
will  remove  the  backing  given  above. 


CHAPTER  XVII. 


PRESERVATIVES  USED  WITH  EMULSIONS. 

Any  emulsion,  washed  or  unwashed,  may  he  used  with  a 
preservative,  which  ensures  the  plates  being  uniformly 
sensitive,  and  also  the  absence  of  those  troublesome  spots 
which  refuse  to  develop.  Colonel  Wortley  says  that  the 
thorough  washing  of  the  film  prevents  the  formation  of 
these  spots ; and  Mr.  Woodbury  never  finds  them  when  he 
dries  his  plates  rapidly  and  at  a fairly  high  temperature. 
The  emulsion  used  by  Woodbury,  however,  contained 
resin,  and  it  may  be  due  to  this  cause  that  he  found  the 
absence  of  these  enemies  to  emulsion  work. 

Beer  Preservative . — The  simplest  preservative  with 
which  tve  we  are  acquainted  is — 

Beer  ...  ...  ...  ...  1 ounce 

Pyrogallic  acid  ...  ...  ...  1 grain 

After  the  plate  is  coated,  it  is  washed  till  all  greasiness 
disappears,  and  the  above  is  flowed  on  the  film,  and 
allowed  to  remain  on  it  for  a minute.  The  beer  solution 
may  then  be  drained  off,  and  the  plate  again  washed,  or 
the  final  washing  may  be  omitted,  and  the  plate  be 
allowed  to  dry  spontaneously.  If  the  plate  be  washed,  it 
should  be  given  a final  rinse  of  distilled  water. 


86 


PRESERVATIVES  USED  WITH  EMULSIONS. 


Mr.  England  recommends,  after  tlie  plate  with  the  beer 
preservative  has  been  dried,  that  it  should  be  washed  and 
given  a final  flooding  with  a pyrogallic  acid  solution,  one 
or  two  grains  to  the  ounce  of  water.  This  procedure,  he 
says,  immensely  increases  the  rapidity  : it  is  rather  more 
trouble  than  the  methods  already  given. 

If  the  beer  be  left  on  the  plate,  and  if  the  dimensions 
of  the  latter  be  more  than  five  by  seven,  a substratum 
(Chap.  XYI.)  should  be  used,  as  the  films  may  have  a 
tendency  to  blister.  It  will  be  found,  however,  if,  after 
exposure , the  plate  be  washed  and  be  allowed  to  dry,  and 
then  be  treated  with  alcohol  and  water  (page  92),  and  be 
developed,  that  the  film  will  adhere  tenaciously  to  the 
plate,  and  that  no  substratum  will  be  requisite. 

Mr.  William  Biooks,  in  the  Photographic  News, 
has  recently  described  a modified  method  of  applying 
the  beer  preservative  to  washed  emulsion  plates. 

The  plate  is  coated  in  the  usual  manner,  and  when 
properly  set  it  is,  ivithout  washing , plunged  into  a bath 
made  as  follows : — 

Bitter  ale...  ...  ...  ...  1 ounce 

Pyrogallic  acid  ...  ...  ...  1 grain 

Sufficient  of  this  is  used  to  fill  a dish  to  a depth  of 

half-an-inch.  The  ale  should  not  be  of  the  kind  known  as 

sweet  or  mild,  as  both  these  contain  too  much  saccharine 
matter.  The  plate  is  left  in  the  preservative  till  there  is 
no  repellent  action  due  to  the  ether  and  alcohol.  It  is  then 
taken  out  and  dried  spontaneously,  a final  warming,  pre- 
vious to  storing,  being  given  to  it  by  means  of  a drying 
oven  or  a hot  water  tin.  The  plates  do  not  require  back- 
ing unless  the  emulsion  be  thin.  The  exposure  necessary 
must  be  ascertained  by  a trial  plate. 

Mr.  Brooks  states  that  he  has  kept  plates  prepared  by 
this  formula  five  months  before  exposure,  and  about  the 
same  time  between  exposure  and  development,  and  has 
developed  them  without  stain  or  speck. 


PRESERVATIVES  USED  WITH  EMULSIONS. 


87 


The  following  preservatives  may  also  be  used  with  the 
emulsion  plates. 

Carey  Lea’s  Preservative . — Mr.  Carey  Lea’s.  u Litmus 
Preservative”  and  tannin  preservatives  are  as  follow  : — 
u Cover  a quarter  of  a pound  of  good  litmus  with  hot 
water ; set  a basin  or  plate  over  the  bowl,  and  put  in  a 
warm  place  for  a day ; throw  the  paste  upon  a filter,  and 
pour  on  hot  water  till  the  filtrate  amounts  to  a quart  (the 
filtration  is  slow)  ; add  a drachm  of  carbolic  acid,  and  the 
litmus  solution  keeps  good  indefinitely. 


Litmus  solution ... 

Water  ... 

Gum-arabic 
Sugar  (fine  white) 

Acetic  acid  (No.  8,  or  Beaufoy’s) 


1 ounce 
6 ounces 
90  grains 


9° 

25  minims 


u The  above  quantity  makes  a convenient  bath  for  a 
GJ  by  8 j-  plate. 

u Throw  the  collodio-bromized  plate  into  a pan  of  water 
until  the  greasy  marks  are  gone,  and  then  pass  it 
into  this  bath,  where  it  should  remain,  with  occasional 
agitation,  about  ten  minutes.  The  time  is  not  important ; 
five  minutes  will  be  sufficient ; fifteen  will  do  no  harm. 

The  tannin  preservative  is  as  follows  : — 


Water  ... 
Gum-arabic 
Sugar 
Tannin  . . . 


...  ounces 
...  90  grains 


The  washing  of  the  plate  is  the  same  as  above. 

Regarding  these  two  preservatives,  Mr.  Lea  says : 
the  litmus  gives  the  softest  and  most  sensitive  plates,  but 
needs  an  intenser  cotton.  The  latter  of  the  two  pre- 
servatives will  work  well  with  a wider  range  of  pyroxy- 
lines  than  the  former,  and  give  a brighter  picture.  The 
tannin  is  the  easiest  to  succeed  with,  but  the  litmus,  when 


88 


PRESERVATIVES  USED  WITH  EMULSIONS. 


well  managed,  undoubtedly  gives  the  best  negatives.  In 
either  case,  the  negatives  are  very  beautiful  ; better 
looking  or  better  printing  negatives  cannot  be  got  with 
the  wet  process.  The  development  may  proceed  by  the 
strong  alkaline  development  (page  91),  or  by  the  practice 
as  described  by  Mr.  Cooper. 

The  Coffee  Preservative . — A coffee  preservative  is  made 
as  follows : — 

1.  — Best  coffee  ...  ...  <..  \ ounce 

White  sugar  ...  ...  90  grains 

Boiling  distilled  or  rain  water  5-J  ounces 

2.  — Gum-arabic  ...  ...  90  grains 

Sugar-candy  ...  ...  20  „ 

Distilled  water  ...  ...  5J  ounces 

When  No.  1 is  cooled,  both  solutions  are  filtered,  and 
the  preservative  applied  by  floating  or  by  immersing  the 
washed  plate  in  a flat  dish  containing  the  solution. 

The  plate  will  require  a substratum  unless  the  precau- 
tion indicated  above  be  observed. 

Tannin  Preservative. — A simple  preservative  is  made 
with  tannin  as  under  : — 

Tannin  (pure)  ...  ...  ...  15  grains 

Distilled  water  ...  ...  ...  1 ounce 


The  plate  is  washed,  and  the  preservative  applied  as 
above. 


Albumen  Beer  Preservative. — The  following  are  pre- 
pared : — 


1.  — Dried  albumen  (or  white  of  egg, 

prepared  as  at  p.  79  1 oz.)...  25 
Water  ...  ...  ...  ...  1 

Liquor  ammonia  ...  ...  i 

2.  — Ordinary  bitter  beer  ...  ...  1 

3.  — Ordinary  bitter  beer  ...  ...  1 

Pyrogailic  acid...  ...  ...  1 


grains 

ounce 

drachm 

ounce 

ounce 

grain 


PRESERVATIVES  USED  WITH  EMULSIONS. 


89 


The  plate,  after  washing,  is  flowed  over  with  equal 
parts  of  1 and  2,  which  are  allowed  to  he  in  contact  with 
the  film  for  one  minute.  It  is  then  thoroughly  washed, 
and  flowed  over  with  No.  3,  and  setup  to  dry. 

These  plates  are  developed  by  any  of  the  alkaline  deve- 
lopers given  in  the  next  chapter.  Reducing  the  amount  of 
pyrogallic  acid  given  to  one-third  will  cause  a thin  nega- 
tive, which  can  be  readily  intensified  by  the  ordinary 
intensifier.  This  preservative  gives  great  beauty  and  deli- 
cacy to  the  negative,  and  subsequent  intensification  is 
better  than  getting  density  by  the  alkaline  developer  alone. 
The  plates  prepared  with  the  albumen  solution  are  exceed- 
ingly rapid  and  safe. 

A substratum  is  required  for  large  plates. 

Col.  Worthy’s  Preservative  is  as  follows,  and  he  recom- 
mends it  as  giving  freedom  from  blisters  often  found  with 
gum  preservatives. 

The  following  stock  solutions  are  prepared : — 

No  1 5 Salicine,  enough  to  make  a saturated  solu- 
< tion  in  distilled  water. 


No.  2. 


Tannin 

Distilled  water 


No 


o (Gallic  acid  ... 
,6'  1 Alcohol 


...  60  grains 
...  1 ounce 

...  48  grains 
...  1 ounce 


To  make  the  preservative,  take  of — 

No.  1 

No.  2. 

No.  3 

Sugar  ... 

Water  ... 


2 ounces 
1 ounce 

l. 

2 

40  grains 
7 ounces 


This  preservative  may  be  used  over  and  over  again  with 
occasional  filtering.  The  plates  are  best  immersed  in  it. 

Bed  Gum  Preservative. — The  following  alcoholic  pre- 
servative may  be  found  useful : — Australian  red  gum,  a 


90 


PRESERVATIVES  USED  WITH  EMULSIONS. 


saturated  solution,  in  equal  parts  of  alcohol  and  water. 
The  plate  is  washed,  flooded  with  equal  parts  of  alcohol 
and  water,  and,  after  the  preservative  is  floated  on,  it  is 
dried  spontaneously.  The  gum  must  be  removed  by 
alcohol  and  water,  and  the  development  will  take  place 
in  the  ordinary  way.  No  substratum  may  be  required. 

Gum  Guiacum  Preservative . — This  preservative  is  really 
mixed  with  the  emulsion  itself.  It  is  prepared  by  making 
a saturated  solution  of  gum  guiacum  in  alcohol  *805. 
One  part  of  this  to  from  20  to  5 parts  of  the  washed  emul- 
sion are  mixed,  and  the  plate  coated  in  the  usual  manner. 
It  is  allowed  to  dry  at  a temperature  of  about  100°,  or  else 
spontaneously.  This  is  an  excellent  addition  to  make  to 
a horny  collodion. 

The  writer  has  tried  the  above  preservatives,  and  has 
therefore  given  them  to  the  reader ; but  there  is  no  doubt 
that  almost  any  of  the  well-known  preservatives  might 
have  been  applied  with  equal  success. 


CHAPTER  XVIII. 


DEVELOPMENT  OF  THE  PLATE. 


For  emulsion  work,  an  alkaline  (or  kindred)  developer 
of  some  kind  is  almost  an  essential,  for  though  faint  detail 
can  be  developed  by  pyrogallic  acid  alone  in  7nost  cases, 
such  a procedure  entails  a prolonged  exposure. 

The  following  are  formulas  for  the  alkaline  developer 
which  the  writer  can  recommend,  having  been  in  use  by 
him  for  several  years  past : 


(1). — Pyrogallic  acid 

...  6 grains 

Water... 

...  1 ounce 

(2). — Potassium  bromide  ... 

...  20  grains 

Water 

...  1 ounce 

(3) . — Anf  monia 

...  1 part 

Water  ... 

...  32  parts 

To  develop,  2 parts  by  measure  of  (1),  2 parts  of  (2), 
and  1 part  of  (3)  are  taken  and  well  mixed  in  the  deve- 
loping cup.  If  an  albumen  or  gum  preservative  be 
used,  No.  2 may  be  reduced  to  1 part. 


The  developer  given  by  Col.  Wortley  is  as  follows  : — 

(a).— Pyrogallic  acid  96  grains 

Methylated  alcohol  ...  ...  1 ounce 


92 


DEVELOPMENT  OF  THE  PLATE. 


(b). — Potassium  bromide  . 


120  grains 
1 ounce 
80  grains 
1 ounce 


Water  distilled 


(c). — Ammonium  carbonate 


Water  ... 


Or. 


(c.) — Liquor  ammonia  *880 6 minims 

Water  ...  ...  ...  ...  1 ounce 

By  the  last  formula,  6 minims  of  (a),  3 minims  of  ( b ), 
and  3 drachms  of  (c)  are  taken  and  mixed. 

M.  Char  don’s  developer  is  as  follows  : — 

1.  — Ammonium  carbonate  ...  ...  10  grains 

Potassium  bromide  ...  ...  2 „ 

Water  ...  ...  ...  ...  1 ounce 

(Care  must  be  taken  that  the  carbonate  is  pure.) 

2.  — Pyrogallic  acid 50  grains 

Alcohol  ...  ...  ...  ...  1 ounce 

To  develop,  the  following  proportions  are  taken  : — 

No.  1 1 ounce 

No.  2 ...  ...  ...  10  to  15  minims 

The  image  will  appear  very  rapidly  if  the  emulsion  has 
been  properly  prepared. 

We  will  now  imagine  that  the  plate  has  been  exposed, 
and  that  we  are  to  develop  the  image.  After  taking  the 
plate  out  ot  the  slide  it  is  carefully  dusted,  and,  if  neces- 
sary, a solution  of  equal  parts  of  alcohol  and  water  is 
flowed  over  it  to  soften  the  film.  It  is  then  either  washed 
under  the  tap,  if  the  water  supply  be  of  good  quality,  or 
is  immersed  in  a dish  of  rain-water  previously  filtered 
through  charcoal.  When  all  repellent  action  between 
the  spirit  and  water  is  obliterated,  the  mixed  proportions 
or  solutions  indicated  above  are  carefully  flowed  over  the 
plate,  and  almost  immediately  poured  back.  The  image 
ought  to  appear  gradually  and  without  veil.  If  it  shows 


DEVELOPMENT  OF  THE  PLATE. 


93 


unwillingness  to  appear,  a fresli  solution  should  be  made, 
omitting  half  the  bromide,  and  this  will  probably  be 
effective. 

To  develop  a plate  having  a preservative,  a little 
thought  should  be  taken  as  to  the  nature  of  the  latter,  as 
has  been  indicated  in  the  last  paragraph.  It  is  evidently 
useless  to  waste  alcohol  if  it  is  not  soluble  in  it.  In  cases 
where  it  is  insoluble,  the  preliminary  flooding  with  the 
spirit  should  be  omitted,  and  the  soluble  matter  entirely 
removed  by  water.  Since  the  object  of  the  alcohol  was  to 
open  the  pores  of  the  collodion,  evidently  the  same  will 
be  accomplished  by  removing  the  soluble  matter  which 
filled  them  up. 

Should  there  not  be  sufficient  density,  resort  must  be 
had  to  the  ordinary  acid  intensifier. 

(1). — Pyrogallic  acid  ...  ...  ...  2 grains 

Citric  acid  ...  ...  ...  2 „ 

Water  ...  ...  ...  ...  1 ounce 


And, 

(2). — Silver  nitrate 
Water 


20  grains 
1 ounce 


The  plate  must  be  well  washed  before  using  this. 
Sufficient  of  No.  1 to  cover  this  plate  should  be  flowed 
over  it,  and  4 or  5 drops  of  No.  2 dropped  into  the  cup, 
and  the  solution  from  off  the  plate  returned  on  to  it. 
The  intensification  should  then  proceed  till  sufficient 
density  is  secured. 

The  developer  which  Mr.  Brooks  recommended  for  his 
process  is  as  follows.  It  is  an  excellent  formula,  and  as 
he  gives  some  valuable  hints  about  conducting  develop- 
ment, which  apply  to  all  processes  alike,  we  give  his 
remarks  in  eoctenso : — 

u After  the  plate  has  been  exposed,  take  it  on  a pneu- 
matic holder,  and  flow  over  it  equal  parts  of  alcohol  and 
water.  I must  here  add  a caution  not  to  use  the  alcohol 


94 


DEVELOPMENT  OF  THE  PLATE. 


too  strong,  or  it  will  attack  the  film  unevenly,  and  cause 
mottling,  especially  in  the  high-lights,  as  I am  sure,  from 
past  experience,  this  is  one  of  the  causes.  It  is  not  seen 
so  much  in  the  half-tone,  and  scarcely  at  all  in  masses 
of  foliage,  or  where  the  subject  is  well  broken  up.  It 
mottling  does  occur,  it  is  most  at  the  thick  end  of  the 
plate.  I do  not  know  if  this  corresponds  with  the  expe- 
rience of  other  workers.  If  the  alcohol  is  used  without 
diluting  (say  of  a s.g.  of  *825)  the  mottled  markings  are 
very  large,  and  as  the  alcohol  is  diluted  with  water,  they 
become  smaller  and  smaller  till  they  disappear  altogether. 
I generally  allow  it  to  soak  well  into  the  film  for  about  two 
minutes,  of  the  strength  mentioned  above  (half  water  and 
half  alcohol).  Methylated  spirit  answers  every  purpose, 
providing  that  it  is  free  from  gum  (if  contaminated  with 
gum  it  turns  milky  on  the  addition  of  water).  If  a quan- 
tity of  plates  are  to  be  developed,  I prefer  to  immerse  each 
plate  in  a tray  containing  the  spirit,  as  it  is  then  done 
effectually.  The  plate  is  then  taken  and  allowed  to  soak 
in  a dish  of  clean  water,  and  rocked  about  until  the  water 
flows  evenly  over  its  surface.  Previous  to  applying  the 
developer,  flood  the  plate  with  the  following : — 

Stock  albumen  (page  79)  ...  1 part 

Water  ...  ...  ...  ...  4 parts 


Allow  this  to  soak  well  into  the  film  ; well  rock  the  plate 
to  ensure  even  action  ; not  less  than  one  minute  must  be 
allowed  for  this  part  of  the  operation.  The  plate  is  then 
slightly  drained,  and  the  alkaline  developer  applied,  made 
from  the  following  stock  solutions  : — 


P. — Pyrogallic  acid  (best)  ... 
Absolute  alcohol 

A. — Sat.  sol.  ammonium  carbonate... 
Potassium  bromide 
Water  ...  , . , 


96  grains 

1 ounce 
4 ounces 

2 drachms 
8 ounces 


A few  drops*of  solution  P for  9 by  8 plates  (say  5 drops), 


DEVELOPMENT  OF  THE  PLATE. 


95 


and  1 ounce  of  solution  A are  mixed  in  a perfectly  clean 
measure,  and  at  once  poured  over  the  plate ; as  soon  as 
it  is  covered  it  must  be  rocked  vigorously  for  a few 
seconds,  so  as  to  make  it  blend  with  the  albumen  on  the 
plate,  and  if  the  plate  has  been  properly  exposed  the  image 
will  at  once  make  its  appearance,  gradually  acquiring 
intensity. 

u After  the  developer  has  been  on  for  some  little  time, 
should  it  apparently  cease  in  its  action,  drain  it  off,  ancl 
again  apply  a little  of  the  prepared  albumen  solution  for 
about  half  a minute ; drain  again,  and  apply  the  alkaline 
developer  as  before : the  image  will  then,  perhaps,  rush 
out  very  rapidly.  This  method  can  be  repeated  as  often 
as  necessary  ; but,  as  a rule,  with  a properly  exposed  plate, 
one  j application  of  the  albumen  is  sufficient.  If  more 
density  is  required,  a drop  or  two  more  of  P solution  can 
be  added.  If  too  much  pyrogallic  is  used,  a very  hard 
negative  is  the  result,  so  it  must  be  used  with  judgment. 
I have  actually  developed  a 24  by  18  plate  to  full  printing 
density  with  only  half  a grain  of  pyrogallic.  The  formula 
given  for  solution  A is  given  for  work  under  normal  con- 
ditions. In  the  winter  time  the  bromide  can  be  reduced 
one-half,  and  in  very  warm  weather  it  can  be  increased. 

11 1 have  used  the  albumen  as  given  above  for  several 
years,  and  the  more  I use  it  the  more  I like  it,  as  it  gives 
an  image  so  much  like  a good  wet  plate  taken  under  the 
best  conditions. 

u Should  it  be  desirable,  the  intensity  can  be  brought 
up  in  the  ordinary  way  before  fixing  with  acid  pyrogallic 
and  silver,  same  as  for  wet  plates.  The  plate  must  be 
well  washed  to  free  it  from  all  traces  of  ammonia,  and 
before  the  silver  is  added  to  the  acid  pyrogallic  it  is  first 
applied  to  the  plate  alone,  which  will  generally  be  suffi- 
cient to  neutralize  whatever  may  have  remained  in  the 
pores  of  the  film.” 

Some  prefer  to  develop  their  plates  in  a dish ; indeed, 
for  ease  of  manipulation,  a dish  is  highly  desirable.  Care 


96  DEVELOPMENT  OF  THE  PLATE. 

must  be  taken  in  this  case  that  sufficient  solution  be  taken 
fully  to  cover  the  plates ; for  an  84  by  6^-  plate,  and  an 
ordinary  10  by  8 porcelain  dish,  4 ounces  will  be  required. 

The  next  developer,  and  that  one  which  seemingly 
will  become  a general  favourite,  is  the  ferrous  oxalate 
developer,  first  formally  introduced  by  Mr.  W.  Willis, 
Jun.,  though  Mr.  Carey  Lea  pointed  out  previously  that 
it  could  be  used. 

The  modes  of  preparing  the  ferrous  oxalate  solution 
will  be  found  in  the  Appendix.  Our  mode  of  procedure 
with  the  developer  is  as  follows  : — If  the  saturated  solu- 
tion of  the  developer  (made  by  dissolving  ferrous  oxalate 
in  a saturated  solution  of  potassium  oxalate)  be  used,  we 
dilute  it  with  half  its  bulk  of  water,  and  add  to  every 
ounce  1 drachm  of  a solution  of  potassium  bromide  in 
water  (20  grains  to  1 ounce),  and  apply  this  to  the  film 
after  washing,  as  described  above.  If  the  image  appears 
slowly,  we  add  half  the  original  quantity  of  the  ferrous 
oxalate  undiluted,  and  then,  if  the  exposure  be  anywhere 
near  correct,  this  will  bring  up  the  requisite  density. 
Should  more  density  be  required,  we  intensify  as  given  at 
page  93. 

Should  the  image  refuse  to  come  out  even  with  the 
stronger  developer,  one  drop  of  a 10  per  cent,  solution  of 
sodium  to  each  ounce  of  hyposulphite  developer  will 
have  an  accelerating  effect  (see  page  19). 

The  exposure  required  for  this  developer  seems  to  be 
about  two-thirds  of  that  required  for  the  alkaline  deve- 
loper given  above,  and  is,  therefore,  a decided  gain  to  the 
photographer. 

There  is  a great  charm  in  this  developer,  the  plates 
gaining  intensity  steadily,  and  without  any  tendency  of 
being  overdone,  and  the  negatives  give  brilliant  prints. 

A modification  of  the  ferrous  oxalate  developer,  which, 
for  the  sake  of  perspicuity,  the  writer  calls  citro-ferrous 
oxalate,  is  also  applicable  for  development.  It  works 
rather  slower,  but  can  be  used  without  the  addition  of 


DEVELOPMENT  OF  THE  PLATE. 


97 


any  bromide.  The  method  ot  preparation  will  he  found  in 
the  Appendix.  The  stronger  solution  there  given  is  used 
without  potassium  bromide,  and  the  development  modified 
and  carried  on  as  above  described  for  the  ferrous  oxalate. 
The  sodium  hyposulphite  may  be  used  with  it  as  with 
the  ferrous  oxalate  developer.  The  ferrous  citrate  deve- 
loper as  introduced  by  Dr.  Eder  is  a very  feeble  deve- 
loper (see  Appendix  for  formula),  whereas  the  ferrous- 
citro-oxalate  is  exceedingly  energetic,  and  is  one  which 
the  writer  can  recommend. 

There  is  another  developer,  originally  introduced  by 
M.  Sammann,  of  Paris,  which  is  popularly  called  the 
u hydrosulphite  developer.”  It  has  not  been  much  em- 
ployed, owing  to  the  trouble  there  is  in  making  it.  It  is, 
however,  very  effective ; and  Mr.  Berkeley  recommends 
it  strongly. 

We  give  M.  Sammann’s  last  directions.  Make  the 
following  stock  solutions  : — 


(1). — Pyrogallic  acid  ...  ...  ...  1 ounce 

Saturated  solution  of  salycilic  acid 

in  water  20  ounces 


(2). — Sodium  bisulphite 
Sodium  sulphite  ... 
Water 


...  1 ounce 

...  80  grains 
...  4 ounces 


20  grains  pf  sodium  borate  may  be  substituted  for  the 
sodium  sulphite. 

When  it  is  required  to  make  the  sodium  hydrosulphite, 
a vial  is  half  filled  with  granulated  zinc,  and  enough  of  (2) 
solution  is  poured  in  to  fill  up  the  interstices.  After 
half-an-hour  the  reaction  is  complete.  The  solution  is 
poured  off  into  a stoppered  bottle,  where  it  will  keep,  but 
only  for  a few  hours. 

The  zinc  and  vial  must  be  well  washed,  in  order  to  be 
ready  for  the  next  quantity  which  may  be  required. 
M.  Sammann  says  that  the  bisulphite  must  be  quite  free 

H 


38 


DEVELOPMENT  OF  THE  PLATE. 


from  sulphurous  acid,  which,  if  present,  must  be  neutralized 
by  sodium  carbonate.  One  part  of  the  bisulphite  should 
dissolve  in  two  of  water  at  the  ordinary  temperature. 

Before  development,  the  plates  are  flooded  with  a solu- 
tion of — 

Tannin  ...  ...  ...  ...  10  grams 

Water  ...  ...  ...  ...  1 ounce 

They  are  then  washed  and  drained.  One  part  of  No.  1 
and  four  parts  of  No.  2 are  then  mixed  together,  and 
placed  in  a dish  containing  the  plate,  which  it  is  just  big 
enough  to  hold.  When  all  the  detail  is  well  out,  it  is 
probable  that  the  negative  will  have  sufficient  printing 
density,  as  the  development  is  very  slow  and  gradual. 
If  the  pyroxyline  be  of  too  u organic  ” a character,  a 
white  veil  is  sometimes  seen  on  the  shadows,  which,  how- 
ever, disappears  on  varnishing.  Intensity,  if  it  be  lack- 
ing, may  be  given  in  the  usual  manner  by  pyrogallic  acid 
and  silver,  according  to  the  formula  given  at  page  93. 
Mr.  Berkeley  states  that  this  developer  may  be  made 
alkaline  with  ammonia,  in  which  case  the  sodium  sulphite 
may  be  omitted. 

The  colour  of  the  negatives  produced  by  the  above 
developers  varies  very  much.  By  the  alkaline  method  we 
may  have  a tint  of  deposit  from  olive  green  to  brick  red ; 
a great  deal,  seemingly,  depends  on  the  fineness  of  the 
original  silver  bromide.  The  finer  it  is  the  redder  will  be 
the  film,  whilst  a black  deposit  is  probably  coarser  than 
any  other.  A deposit  which  is  bluish  when  viewed  by 
transmitted  light  is  probably  intermediate  between  the 
two,  an  olive  green  tint  again  lying  between  the  reddish 
and  the  blue. 

The  ferrous  oxalate  and  ferrous-citro-oxalate  developer 
gives  a blue  black  deposit,  as  a rule,  and  is  coarser  than 
that  given  by  the  alkaline  or  hydrosulphite  developer. 
The  rapidity  of  development  must  also  influence  the 
-colour,  since  whatever  method  be  adopted,  the  metallic 


DEVELOPMENT  OF  THE  PLATE. 


99 


silver  is  deposited,  as  well  as  reduced,  more  particularly 
in  the  alkaline  method. 

A negative  that  is  fully  developed  by  any  of  these 
methods  should  show  reduced  silver  bromide  next  to  the 
glass  plate  in  the  most  opaque  parts ; so  complete  should 
this  be,  that  if  the  image  be  dissolved  away  by  nitric  acid, 
we  should  have  a positive  picture  left  behind  formed  of 
unaltered  bromide,  having  perfect  gradation. 

In  the  early  days  of  emulsion  making  a weaker  developer 
was  made  use  of,  and  as  for  some  plates  it  is  still  useful, 
we  insert  it  here  for  the  guidance  of  students. 

No.  1. — Pyrogallic  acid  ...  ...  3 grains 

Water...  ...  ...  ...  1 ounce 

(This  will  not  keep  long,  but  should  be  made  when  re- 
quired.) 


No.  2. — Ammonium  carbonate 

...  1^- drachms 

Water... 

1 ounce 

Or, 

No.  2. — Liquor  ammonia 

...  1 part 

Water 

...  12  parts 

No.  3. — Potassium  bromide  ... 

...  1 grain 

Water 

...  1 ounce 

No.  4. — Silver  nitrate 

...  20  grains 

Citric  acid  ... 

25 

...  ,, 

Water 

...  1 ounce 

Nos.  2,  3,  and  4 will  keep  infinitely. 

The  film  should  then  be  well  washed  under  the  tap.  If 
there  be  every  reason  to  suppose  that  proper  exposure  has 
been  given,  make  a developing  mixture  in  the  following 
proportion : — 

No.  1 ... 

No.  2 ... 


1 drachm 
1 drop 


100 


DEVELOPMENT  OF  THE  PLATE. 


Sufficient  should  be  taken  to  well  cover  the  plate.  Nos. 
2 and  3 should  be  first  dropped  into  the  developing  cup, 
and  finally  No.  1 is  added.  (The  necessity  of  stirring  is 
prevented  by  this  procedure.)  Flood  this  over  the  plate. 
The  image,  if  everything  be  en  regie , should  appear  quickly, 
and  the  developer  should  be  worked  over  the  plate  till  all 
detail  appears  by  reflected  light.  When  this  happens, 
another  drop  of  No.  2 to  each  drachm  should  be  dropped 
into  the  measure,  and  the  solution  poured  back  onto  it  as 
before,  and  the  intensification  with  the  stronger  ammoni- 
acal  solution  proceeded  with.  The  intensity  will  gradually 
be  increased,  and  it  may  happen  that  the  requisite  density 
will  be  obtained.  Should  the  density  not  be  sufficient, 
one  drop  of  No.  4,  with  a drachm  of  No.  1,  maybe  mixed, 
and  intensification  takes  place  in  the  ordinary  manner. 
In  the  writer’s  experience,  the  colour  and  printing  quali- 
ties of  all  negatives  by  this  process  are  improved  by 
even  a slight  application  of  the  intensifier. 

Should  the  negative  flash  out  at  once  on  the  application 
of  the  first  developer,  it  is  a sign  of  over-exposure  of  the 
plate.  The  developer  should  immediately  be  returned  to 
the  cup,  and  the  plate  washed.  Two  drops  extra  of  No.  3 
must  be  added  to  the  developer,  and  the  development  pro- 
ceeded with  as  before.  The  potassium  bromide  keeps 
the  shadows  bright,  and  acts  as  a retarder ; so  much  has  it 
the  latter  qualification,  that  if  a large  quantity  be  added, 
the  plate  will  refuse  to  develop  at  all.  It  is  better  to  fix 
an  over-exposed  picture  immediately  the  detail  is  all  out, 
and  intensify  with  pyrogallic  acid  and  silver  afterwards. 

If  traces  of  the  picture  refuse  to  appear  in  three  or  four 
seconds  after  an  application  of  the  primary  developer, 
a fresh  developer  should  be  made  up  similar  to  the  above, 
omitting  the  bromide  of  potassium.  If  the  picture  refuse 
to  appear  satisfactorily  when  this  course  is  adopted,  the 
plate  is  hopelessly  under-exposed.  When  the  detail  is 
well  out,  the  intensification  should  be  carried  on  as  given 
at  page  93. 


DEVELOPMENT  OF  THE  PLATE. 


101 


Fixing  Solution. — The  negative  should  be  fixed  with 
potassium  cyanide  or  sodium  hyposulphite. 

Potassium  cyanide  25  grains 

Water  1 ounce 


Or, 

Sodium  hyposulphite  ... 
Water  


1 ounce 
6 ounces 


The  first  may  be  flowed  over  the  plate,  but  a dipping 
bath  for  the  latter  will  be  found  advantageous  for  studio 
work.  There  are  some  images  which  will  not  stand  the 
cyanide,  and  in  rare  instances  some  will  not  stand  pro- 
longed immersion  in  the  hyposulphite ; it  may  be  because 
the  metallic  silver  is  in  a very  fine  state  of  division.  This 
seems  all  the  more  probable  since  we  know  that  in  this 
state  it  is  attacked  by  the  cyanide.  When  all  the  bromide 
is  dissolved  from  out  of  the  film,  the  plate  should  be  well 
washed  back  and  front.  It  is  not  amiss  to  give  a dip  in 
u solution  of  alum,  as  used  for  gelatine  plates,  if  hypo- 
sulphite has  been  used,  since  it  effectually  decomposes  it. 


CHAPTER  XIX. 


A MOIST  EMULSION  PROCESS. 

Mr.  Mawdsley,  in  December,  1876,  introduced  a moist 
emulsion  process  which  he  states  gives  very  certain 
results,  and,  when  used  with  a tent,  or  its  equivalent, 
is  admirable,  as  it  allows  the  plates  to  be  prepared 
ready  for  use  at  home,  and  the  negatives  may  be  developed 
in  the  field  with  the  minimum  amount  of  solutions.  Washed 
emulsion  may  be  employed  advantageously.  After  coat- 
ing the  plate  it  is  rinsed  with  water,  and  the  following 
solution  poured  over  it : — 

Glycerine  (Price’s)  ...  ...  1 ounce 

Albumen  (white  of  egg)  ...  1 „ 

Water  ...  ...  20  ounces 

These  proportions  are  recommended  when  the  plates 
are  to  be  used  shortly  after  preparation.  If  they  are  to 
be  kept  (say)  a fortnight  or  three  weeks,  the  following 
may  be  used : — 

Glycerine  (Price’s)  ...  ...  2 ounces 

Albumen  ...  * 1 ounce 

Water  6 ounces 

In  both  cases  fifty  grains  of  dried  albumen  dissolved 
in  one  ounce  of  water  may  be  employed  instead  of  the  white 


A MOIST  EMULSION  PROCESS. 


103 


of  egg.  Tlie  time  of  exposure  by  tliis  method  is  the  same 
as  that  required  by  the  dried  plate. 

The  development  that  Mr.  Mawdsley  recommends  is  as 
follows  : — 

The  plate  is  flushed  with — 

Saturated  solution  of  ammonium 

carbonate  ...  ...  ...  1 part 

Water  ...  ...  ...  ...  ...  1 „ 

This  is  returned  to  the  bottle  for  future  use. 

An  eight-grain  solution  of  pyrogallic  acid  is  then  poured 
over  the  plate,  with  a few  drops  of  a ten-grain  solution  of 
potassium  bromide  to  act  as  a restrainer. 

When  the  details  are  well  out,  the  plate  is  flooded  with 

Water  ...  ...  ...  ...  5 ounces 

Acetic  acid...  ...  ...  ...  2 drachms 

This  neutralizes  the  ammonia  and  arrests  development. 
The  plate  is  now  stowed  away  in  a light-tight  box,  and 
kept  for  intensification,  &c.,  at  home.  If  under-exposed, 
or  properly  exposed,  the  plate  is  intensified  after  washing 
and  flooding  with  acidulated  water,  and  fixed.  If  over- 
exposed, it  is  first  fixed,  and  then  intensified. 

This  process  is  simple  where  it  is  desired  to  develop 
pictures  on  the  spot.  One  4-ounce  bottle,  two  8-ounce 
bottles,  and  one  2-ounce  bottle  will  contain  all  the 
chemicals  and  wash-water  that  may  be  required  in  the 
field  in  order  to  develop  one  and  a-half  dozen  plates. 


CHAPTER  XX. 


COLLODIO-CHLORIDE  EMULSION  FOR 
DEVELOPMENT. 


In  the  previous  processes  it  will  be  seen  that  silver  bro- 
mide forms  the  staple  sensitive  salt,  though  both  iodide 
and  chloride  have  been  introduced  into  the  emulsion,  but 
in  small  quantities.  The  use  of  chloride  by  itself  has,  till 
quite  recently,  been  inadmissable,  on  account  of  the  diffi- 
culty of  producing  a chemical  developer  suitable  for  it. 
Dr.  Eder  and  Captain  Pizzighelli  found  that  for  gelatino- 
chloride  plates,  ferrous  citrate  in  a weak  form  gave  good 
development.  The  developer  was  very  weak,  however,  in 
the  form  they  gave  (see  Appendix),  and  the  writer  intro- 
duced the  ferrous-citro-oxalate  form,  which  has  proved 
suitable  for  collodio-chloride  plates. 

There  are  two  formulas  for  collodio-chloride  emulsions, 
one  with  excess  of  silver,  and  the  other  with  an  excess  of 
chloride.  E or  most  purposes  the  latter  is  the  one  we  pre- 
fer, since  it  can  be  made  and  used  in  a quarter  of  an  hour 
when  required.  What  is  usually  called  collodio-chloride 
is  totally  unfit  for  chemical  development,  and  it  is  mis- 
leading to  class  it  under  this  denomination,  since  it  has  a 
large  proportion  of  citrate  in  its  composition.  To  make 
the  collodio-chloride  we  proceed  as  follows  : — 


COLLODIO-CHLORIDE  EMULSION. 


105 


Weigh  out  the  following — 
Pyroxyline  (any  easily  soluble  sort) 

.33  33  33  33  33 

Calcium  chloride  ... 

Silver  nitrate 


10  grains 

^ 33 

20  „ 

50  „ 


Dissolve  the  calcium  chloride  in  \ ounce  of  alcohol  *805, 
by  warming  over  a spirit  lamp.  Place  the  5 grains  of 
pyroxyline  in  a 2-ounce  bottle,  and  pour  on  it  the  alcohol 
containing  the  calcium.  After  a couple  of  minutes  add 
£ ounce  of  ether,  when  the  cotton  will  dissolve. 

Dissolve  the  50  grains  of  silver  nitrate  in  a test-tube  in 
the  smallest  quantity  of  water,  and  add  to  it  1 ounce  of 
boiling  alcohol  ’805,  and  mix.  Previous  to  this  the 
10  grains  of  pyroxyline  should  have  been  placed  in  a four- 
ounce  bottle,  and  the  alcohol  containing  the  silver  should 
be  poured  on.  Next  add  1 ounce  of  ether,  little  by  little, 
with  continuous  shaking.  The  silver  nitrate  may  very 
probably  partially  crystallize  out,  but  that  is  of  very  little 
consequence.  Take  the  two  bottles  into  the  dark-room  (a 
room  glazed  for  wet-plate  work  will  answer  perfectly),  and 
pour  gradually  the  calcium  chloride  collodion  into  the  silver 
nitrate  collodion — on  no  account  vice  versa.  The  resulting 
emulsion,  of  course,  is  silver  chloride  in  an  extremely  fine 
state  of  division.  A plate  coated  with  it  should  show 
a canary  colour  by  transmitted  skylight,  and  a thickish 
film  should  make  a gas  flame  appear  ruby-coloured. 
The  emulsion  may  be  washed  in  the  usual  way,  if  required 
(see  page  51)  ; but,  when  washed,  and  used  simply  dried 
after  washing,  it  is,  like  other  collodion  emulsion  prepared 
with  an  excess  of  haloid,  rather  insensitive.  Before  doing 
anything  with  the  emulsion,  however,  a plate  should  be 
coated,  washed  under  a tap,  and  placed  in  the  dark  slide. 
The  slide  should  be  taken  into  white  light,  and  half  the 
front  pulled  up  for  a second,  and  then  closed.  Ferrous- 
citro-oxalate  developer,  as  given  in  the  Appendix,  should 
then  be  applied,  and  the  result  noted.  A blackening  of 


106 


COLLODIO-CHLORIDE  EMULSION. 


the  film  may  ensue.  If  correct  on  the  application  of  the 
developer,  the  film  should  not  show  any  reduction  of  the 
chloride,  except  on  the  exposed  half  of  the  plate.  Should 
blackening  take  place,  nitric  acid  may  be  added ; but  that 
rather  rots  the  film  if  kept  too  long  in  contact  with  the 
emulsion,  which  would  be  the  case  if  it  is  to  remain  un- 
washed. A simpler  plan  is  to  add  a soluble  chloride  which 
would  form  a double  chloride.  Three  or  four  drops  of  a 
20-grain  solution  of  cupric  chloride  (chloride  of  copper) 
should  be  added  to  the  emulsion,  and  shaken  up,  and 
immediately  the  fog  disappears.  Two  or  three  drops  of 
gold  tri-chloride,  or  of  cobaltic  chloride  of  a similar 
strength  as  the  copper  chloride,  would  answer  equally  as 
well. 

So  far  as  regards  the  making  of  the  emulsion.  The 
next  point  is  the  preparation  of  the  plates.  As  was  said 
before,  it  can  be  washed,  but  we  really  see  no  advantage 
in  so  doing.  Polished  and  edged  plates  [(see  page  77) 
may  be  coated,  washed,  and  then  simply  flooded  once 
over  with — 

Beer  ...  ...  5 ounces 

Sugar  (white)  ...  1 moderate  sized  lump 

Pyrogallic  acid  ....  ...  ...  5 grains 

These,  when  dry,  will  be  very  sensitive,  and  put  to  shame 
many  a collodio-bromide  emulsion.  Any  of  the  preserva- 
tives given  in  Chap.  XVII.  may  also  be  used.  To  develop, 
rinse,  and  then  simply  immerse  them  in  a dish  containing 
the  ferrous-citro-oxalate.  In  a short  time  the  image  will 
begin  to  appear,  and  gradually  gain  strength.  The 
colour  of  the  image  is  a beautiful  ivory  black,  and  admir- 
ably suited  for  collodion  transfers.  If  a warmer  tint  is 
required,  tone  in  a dish  with — 

Uranium  nitrate ...  ...  ...  10  grains 

Ferricyanide  of  potassium  ...  10  „ 

Water 10  ounces 


COLLODIO-CHLORIDE  EMULSION. 


107 


The  colour  will  rapidly  warm,  and  would  eventually 
become  a pretty  chocolate  colour. 

It  will  be  noted  that  an  emulsion  prepared  in  this  way 
may  be  developed  by  the  ferrous-citro-oxalate  without 
any  restrainer. 

They  will  also  develop  with  : — 

Hydrokinone  ...  ...  ...  10  grains 

Water  ...  ...  ...  ...  1 ounce 

to  every  ounce  of  which  are  added  3 or  4 drops  of  a 
saturated  solution  of  carbonate  of  ammonia. 

The  emulsion  may  also  be  made  with  an  excess  of 
silver  nitrate,  in  which  case,  in  the  above  formulae,  seventy 
grains  of  silver  nitrate  should  be  used.  Fog  may  be 
prevented  by  adding  2 or  3 drops  of  strong  nitric  acid  to 
the  calcium  chloride  collodion,  or  it  may  be  eliminated  by 
the  use  ot  bichromate  of  potash,  or  by  hydrochloric  acid, 
or  by  cupric  cobaltic,  or  auric  (gold)  chlorides,  after  the 
excess  of  silver  has  been  washed  away.  In  fact,  the 
same  procedure  should  be  adopted  as  in  the  collodio- 
bromide  process  (see  Chap.  VII.)  The  development 
of  this  emulsion  is  carried  on  as  above. 

Collodio-bromo-chloride  Emulsion. — A very  capital 

emulsion  is  formed  by  mixing  § part  of  an  unwashed 
collodio-bromide  emulsion  with  ^ part  of  an  unwashed 
collodio-chloride  emulsion.  The  same  proportion  of 
washed  emulsions  may  also  be  mixed  with  advantage. 
The  development  of  this  emulsion  is  most  advantageous 
when  an  unrestrained  developer  such  as  the  above  is 
used. 


CHAPTER  XXL 


DEFECTS  IN  COLLODION  EMULSION  PLATES. 

It  is  somewhat  difficult  to  name  the  especial  defects 
found  in  the  emulsion  dry  plates,  hut  we  will  endeavour 
to  point  out  the  principal  ones. 

Blisters  in  the  film  may  he  due  to  a preservative,  more 
particularly  if  it  contain  gummy  matter.  Thus,  with  the 
beer,  or  the  gum-gallic,  or  coffee  preservatives  these  may 
make  their  appearance.  The  remedy  has  already  heen 
given. 

Black  spots  on  development  are  usually  due  to  dust  being 
allowed  to  settle  on  the  film  whilst  drying  ; decomposing 
organic  matter  in  fine  particles  is  also  a fruitful  source  of 
these  annoyances. 

Insensitive  patches  or  spots  on  development  have  not  yet 
heen  tracked  to  an  origin  ; hut  if  a preservative  he  em- 
ployed, they  will  rarely  he  met  with.  They  seem  to  he 
due  to  impurities  in  the  pyroxyline,  since  with  certain 
preparations  they  are  altogether  absent. 

Crape  markings  in  the  film  are  usually  due  to  the  solvents 
of  the  emulsion  being  too  aqueous  ; or  they  may  he  due 
to  the  emulsion  not  having  heen  shaken  up  shortly  before 
being  used,  or  to  the  bromide  being  too  coarse. 

Thin  transparent  films  with  washed  emulsion  are  usually 
due  to  the  last  two  causes. 

Ihe  emulsion  refusing  to  flow  properly  is  due  to  deficiency 


DEFECTS  IN  EMULSION  PLATES. 


109 


of  solvents.  This  is  frequently  met  with  if  the  same  emul- 
sion be  used  for  coating  many  plates.  It  should  be  diluted 
down  with  1 part  of  alcohol  (*812)  to  2 of  ether  (*720). 

When  the  film  tends  to  peel  off  the  plate , the  pyroxyline  is 
probably  of  too  contractile  and  horny  a nature,  in  which 
case  the  proper  treatment  is  to  mix  it  with  an  emulsion 
made  with  one  of  a more  powdery  character,  or  to  mix  a 
little  gum  guiacum  dissolved  in  alcohol  with  it. 

Circular  insensitive  patches  in  the  centre  of  the  plates  are 
sometimes  met  with  in  hot  weather,  when  a pneumatic 
plate-holder  is  used. 

The  cause  of  fog  has  been  pointed  out  in  the  first 
chapter,  and  need  scarcely  be  alluded  to  again.  To 
eliminate  it  in  a washed  emulsion,  the  careful  addition  of 
a few  drops  of  a dilute  solution  of  iodine  in  alcohol  will 
prove  effective.  With  such  an  emulsion,  when  used 
with  a preservative,  a dip  in  a 10  per  cent,  solution  of 
hydrochloric  acid  in  water  will  eliminate  all  fog.  In  an 
unwashed  emulsion  the  addition  of  nitric  acid  will  effect 
a cure. 

Plates  ivhich  fog  through  having  been  exposed  to  light 
may  be  rendered  available  for  use  by  washing  off  any 
preservative  they  may  have  on  them,  and  immersing  them 
in  a hock-coloured  solution  of  potassium  bichromate,  or 
by  water  faintly  tinged  with  potassium  permanganate,  or 
with  a 10  per  cent,  solution  of  hydroxyl  or  hydrochloric 
acid  in  water.  After  washing,  a preservative  may  again 
be  applied. 

Plates  which  jog  under  development , when  the  emulsion  is 
not  in  fault,  must  owe  this  defect  to  one  of  two  causes  : 
1st,  to  the  light  of  the  developing  room  ; or,  2nd,  to  the 
developer.  The  first  cause  is  easily  tracked,  as  a plate 
may  be  prepared  and  developed  in  almost  absolute 
darkness  without  receiving  any  exposure  to  ordinary 
light.  If,  after  a short  application  of  the  developer,  no 
fog  is  found,  the  light  used  during  development  is  in 
fault.  If  the  plate  fogs,  the  developer  is  wrong.  In  this 


110 


DEFECTS  IN  EMULSION  PLATES. 


case,  try  making  up  fresh  solutions,  and  using  more 
soluble  bromide  as  a restrainer.  With  the  ferrous  oxalate 
developer  want  of  bromide  is  often  the  cause  of  fog. 

Drying  markings  in  a film  are  sometimes  met  with.  They 
generally  form  a sort  of  ripple  marking  near  one  edge. 
They  are  usually  found  when  impure  water  is  used  for 
the  final  washing  of  a plate,  and  are  absent  when  a final 
rinsing  with  distilled  water  is  given.  With  plain 
washed  emulsion  these  markings  are  never  met  with 
unless  the  temperature  of  the  drying  oven  is  high. 

Thick  specks  in  a plate  are  usually  due  to  the  dried 
emulsion  from  the  neck  of  the  bottle  mixing  with 
the  solution  and  finding  a resting-place  in  the  film. 


CHAPTER  XXII. 


INTRODUCTORY  REMARKS  ON  GELATINE 
EMULSIONS. 

A gelatine  emulsion,  as  it  is  somewhat  crudely  called, 
is  in  reality  silver  bromide,  &c.,  emulsified  in  a gelatine 
solution,  with  which  plates  are  coated.  We  have  already 
(page  3)  stated  that  there  are  various  modifications  of 
the  molecular  state  of  the  bromide,  and  that  some  can  be 
brought  about  in  a variety  of  ways.  Mr.  C.  Bennett  first 
showed  how  extremely  sensitive  plates  would  be  prepared 
by  keeping  the  gelatine  solution  liquid  at  a temperature  of 
about  90°  for  six  or  seven  days.  What  he  accomplished 
was  in  reality  to  bring  about  a modification  which  was 
very  easily  acted  upon  by  light.  It  need  scarcely  be  said 
that  in  certain  states  of  the  weather  this  long  emulsification 
was  attended  with  enormous  risks  of  decomposing  the 
gelatine,  and  when  gelatine  decomposes,  the  products  are 
apt  to  reduce  the  silver  bromide  to  the  metallic  state,  and 
hence  to  cause  fog.  Besides  this,  there  is  the  danger,  even 
if  fog  is  not  produced,  of  the  gelatine  refusing  to  set. 
Col.  Wortley  stated  that  he  got  the  same  rapidity  in  his 
plates  by  raising  the  temperature  of  the  emulsion  for  a few 
hours  to  150°  F.,  and  Mr.  Mansfield  first  recommended  the 
gelatine  emulsion  to  be  brought  to  the  boiling  point ; but 
then  a very  short  boiling  is  liable  to  destroy  the  setting 
qualities  of  the  gelatine.  Mr.  W.  B.  Bolton,  in  an  article 


112 


REMARKS  ON  GELATINE  EMULSIONS. 


in  the  British  Journal  of  Photography , first  indicated  the 
true  method  of  preparing  emulsions  by  boiling.  He 
emulsified  in  a small  quantity  of  gelatine,  boiled,  and  then 
added  to  the  emulsion  the  proper  quantity  of  gelatine  to 
give  it  a firm  consistency  when  setting.  We  may  say 
that  the  publication  of  this  article  opened  out  a new  era 
in  gelatine  emulsions.  We  need  not  explain  the  rationale 
of  the  process  further.  Dr.  Van  Monckhoven  called  atten- 
tion to  the  fact  that  by  adding  ammonia  to  the  silver 
bromide  a modification  was  obtained  which  gave  great 
rapidity,  and  Dr.  Eder  carried  the  principle  further,  and 
gave  a really  workable,  though  in  some  states  of  weather 
a dangerous,  process.  The  great  desideratum , according  to 
these  authorities,  was  to  obtain  a grey  emulsion  by  trans- 
mitted light,  and  green  by  reflected ; but,  as  will  be  seen 
from  our  remarks  on  page  3,  this  state  is  not  what  we  con- 
sider the  most  sensitive,  and  certainly  we  have  never  ob- 
tained plates  so  rapid  by  the  ammonia  process  as  we  have 
by'the  boiling  process.  The  addition  of  the  ammonia  is,  as 
we  have  remarked,  dangerous  sometimes,  since  its  presence 
is  very  apt  to  induce  fog,  owing  to  gelatine  decomposing 
more  rapidly  in  its  presence.  We  have  endeavoured  in 
the  following  pages  to  give  an  accurate  description  of  the 
way  to  carry  out  all  these  processes.  But  we  here  make 
a distinct  record  of  our  opinion,  which  is,  that  for  rapidity 
and  certainty  the  boiling  processes  are  the  best  and  safest. 

We  have  also  given  processes  for  precipitating  silver 
bromide  in  water  or  glycerine  and  water,  and  then  adding 
it  to  gelatine.  The  processes  are  effective,  but  they  are 
not  so  easily  employed  where  iodide  is  used,  as  the  iodide 
is  apt  to  settle  down  in  large  particles. 

There  is  a vast  amount  of  experimental  work  to  be 
carried  out  in  all  the  gelatine  processes.  One  simple  ex- 
periment we  would  wish  our  readers  to  try,  and  that  is  to 
prepare  gelatine  emulsions  with  silver  iodide  alone,  bro- 
mide alone,  and  chloride  alone,  and  to  mix  the  three  in 
different  proportions,  and  to  note  the  results.  We  are 


EEMAEKS  ON  GELATINE  EMULSIONS. 


113 


sure  that  the  relative  value  of  the  different  emulsions  will 
he  very  soon  apparent.  It  is  very  easy  to  try  and  write 
or  talk  down  a process,  and  in  some  cases  we  feel  that 
this  has  been  done.  The  only  fair  way  of  settling  the 
value  of  a process  is  for  the  individual  to  try  the  experi- 
ments himself,  and  form  his  own  judgment ; but  if  the 
reader  has  a process  with  which  he  is  thoroughly  satisfied, 
we  advise  him  to  keep  to  it,  and  not  waste  his  time  or 
energy  in  following  out  more  elaborate,  but  perhaps  less 
successful,  processes. 

A pertinent  question  for  everyone  to  ask  himself  is,  as 
to  whether  a very  rapid  process  is  always  a desideratum. 
For  our  own  part  we  unhesitatingly  say  it  is  not.  For 
transient  effects  in  a landscape  for  instantaneous  views,  or 
for  portraiture  in  dull  weather,  rapid  plates  are  useful  ad- 
juncts, but  should  be  nothing  more.  We  believe  that 
finer  pictures,  more  mellow  and  truthful,  are  usually 
produced  by  the  slower  plates,  be  they  collodion  or 
gelatine. 


CHAPTER  XXIII. 


ON  THE  CAUSES  OF  SENSITIVENESS  IN  GELATINE 
EMULSION. 

It  would  have  been  difficult  to  have  treated  of  the  causes 
which  induce  sensitiveness  in  gelatine  emulsion  in  the 
same  chapter  as  that  which  treats  of  the  sensitiveness  in 
collodion  emulsion  ; we  therefore  determined  to  postpone 
their  consideration  till  now.  It  may  be  said  that  in  a gela- 
tine emulsion  it  is  almost  necessary  that  the  soluble  bro- 
mide be  in  excess  over  the  silver  nitrate  ; that  is,  that 
when  all  the  nitrate  is  converted  into  bromide,  there  should 
still  be  soluble  bromide  left  in  solution.  It  must  be  recol- 
lected that  gelatine  is  a most  unstable  body,  and  we 
believe  we  are  correct  in  saying  that  from  the  first 
time  it  is  heated  its  decomposition  commences.  This 
decomposition  at  first  gives  rise  to  an  acid  reaction,  and 
eventually  to  an  alkaline  one.  In  the  first  stage  no  harm 
will  ensue  to  silver  bromide  suspended  in  it ; but  when  the 
latter  stage  is  arrived  at,  there  is  a great  tendency  for  the 
silver  salt  to  be  reduced  to  the  metallic  state,  unless  some 
body  be  present  which  hinders  it.  Such  bodies  are  found 
in  acids  and  soluble  bromide.  The  addition  of  acid  must 
be  made  cautiously,  since  acids  cause  gelatine  to  lose  its 
setting  properties,  and  there  is,  consequently,  a greater 
safety  in  using  excess  of  bromide.  Again,  if  there 
were  any  excess  of  silver  nitrate,  it  would  combine 


SENSITIVENESS  IN  GELATINE  EMULSION.  115 


with  the  gelatine,  and  we  should  have  a product  formed 
not  particularly  sensitive  to  light,  but  acted  upon  by  a 
developer  at  once,  and  have  in  consequence  a production 
of  red  fog.  We  may,  therefore,  take  it  that  in  the  pro- 
duction of  gelatine  emulsion  an  excess  of  soluble  bromide 
is  essential. 

In  the  first  chapter  we  have  already  referred  to  the 
differences  in  molecular  structure  that  silver  bromide 
may  assume  ; and  we  repeat  that  the  molecular  structure 
is  purely  due  to  physical  causes,  and  not  to  different 
chemical  composition  ; in  other  words,  bromide,  chloride, 
and  iodide  of  silver  have  always  the  same  proportions  of 
bromine,  chlorine,  and  iodine  to  silver  present. 

When  silver  bromide  is  produced  with  proper  precau- 
tions as  an  emulsion,  or  by  the  bath,  as  in  the  wet  collo- 
dion process,  we  have  the  film  transmitting  red  raj^s,  and 
absorbing  the  blue  rays  ; showing  that  the  work  performed 
in  the  film  is  really  done  by  the  blue  rays.  If  a gelatine 
emulsion,  however,  be  boiled,  the  bromide,  unless  great 
care  be  taken  in  mixing,  becomes  a cold  grey  colour  by 
transmitted  light,  and  yellowish  green  by  reflected  light, 
and  this  shows  that  some  of  the  yellow  and  red  rays  are 
absorbed,  whilst  some  of  the  blue  rays  are  transmitted ; and 
yet  it  is  found  that  this  silver  bromide  is  more  sensitive  to 
the  blue  rays  than  the  redder  form.  Can  any  explanation 
be  given  of  this?  We  think  it  can.  It  is  not  owing  to 
the  fact  that  the  silver  salt  is  slightly  sensitive  to  the 
yellow  rays,  for  this  would  only  increase  the  sensitive- 
ness by  about  one-twentieth,  as  photographing  the 
spectrum  shows  us.  It  must  be  recollected  that  the 
apparent  colour  of  the  bromide  may  be  produced  in  two 
ways — or  rather,  that  it  may  be  due  to  two  causes  : it  may 
be  due  to  the  colour  of  the  silver  bromide  itself,  which  is 
what  we  may  call  its  molecular  colour,  or  a variation  in 
colour  may  be  due  to  the  scattering  of  light  by  the 
different  sizes  of  the  particles,  each  particle  being  pro- 
bably composed  of  thousands  of  molecules.  When  an 


116  SENSITIVENESS  IN  GELATINE  EMULSION. 


emulsion  is  boiled,  an  inspection  of  the  films  after 
different  lengths  of  boiling  will  convince  us  that  the 
longer  an  emulsion  is  boiled,  the  larger  the  size  of  the 
particles  which  are  embedded  in  the  gelatine.  Hence 
boiling  produces  large  particles.  Now,  we  have  shown 
(page  17)  that  metallic  silver  cannot  exist  in  contact  with 
silver  bromide,  but  that  the  latter  becomes  at  once 
amenable  to  development  by  its  conversion  into  sub- 
bromide. Suppose,  then,  that  one  molecule  of  one  of 
these  particles  is  affected  by  light,  the  rest  of  the 
particle  would  be  reduced  and  give  the  appearance  of 
increased  sensitiveness,  and  would  practically  have  that  in- 
creased sensitiveness,  since  sensitiveness  is  only  recognized 
by  a visible  quantity  of  metallic  silver.  Thus,  if  the 
particles  in  one  were  only  one-tenth  part  of  the  size  they 
are  in  another,  it  is  quite  within  the  range  of  probability 
that  the  sensitiveness  of  the  former  might  be  concluded 
to  be  only  one-tenth  of  the  latter,  whereas  the  light  would 
have  done  precisely  the  same  work  on  the  two.  Let  us 
take  an  example  of  two  kinds  of  bromide,  both  apparently 
having  the  same  size  of  particles,  the  one  having  been  pro- 
duced originally  in  the  orange  state,  which  the  spectro- 
scope tells  us  is  peculiarly  sensitive  to  the  blue  rays,  and 
the  other  in  a different  molecular  state,  which  the  spectro- 
scope tells  us  is  sensitive  to  the  red,  but  much  less  sensitive 
to  the  blue  than  the  first  sort.  It  will  be  found  that,  after 
boiling  these  two  emulsions,  the  same  ratio  of  sensitiveness 
to  the  blue  end  of  the  spectrum  is  still  maintained,  and  if 
two  plates  prepared  by  the  two  emulsions  be  carefully 
examined  by  transmitted  light,  it  will  be  found  that  the 
emulsion  which  was  originally  of  an  orange  tint  still  shows 
a trace  of  orange  colour  mixed  up  with  the  grey ; in  other 
words,  there  is  a mixture  of  the  scattered  light,  and  of  the 
true  molecular  colour.  In  order,  then,  to  have  the  greatest 
sensitiveness,  the  first  condition  is  that  the  original  emul- 
sion before  boiling  must  be  orange  by  transmitted  light. 

There  is  another  point  in  regard  to  the  boiling  of  an 


SENSITIVENESS  IN  GELATINE  EMULSION. 


117 


emulsion,  which  is,  that  silver  bromide  is  slightly  soluble 
in  water,  and  much  more  so  in  water  containing  soluble 
bromide.  Without  doubt  during  boiling  some  portions 
of  the  silver  bromide  are  dissolved  and  re-precipitated, 
other  portions  of  the  bromide  being  taken  up,  and  they 
in  their  turn  deposited,  and  so  on. 

Mr.  Wilson,  in  his  description  of  his  gelatine  process 
(which  won  the  Paget  prize),  and  which  statement  we 
overlooked  when  we  experimented  on  the  subject, 
says : — 

u The  proportions  of  soluble  bromide  and  silver  nitrate  are 
very  important.  Contrary  to  usual  statements,  the  larger 
the  excess  of  silver  bromide,  the  more  quickly  is  the  AgBr 
converted ; if  there  be  but  little  excess,  a very  long  cook- 
ing will  be  required  ; and  if  exactly  the  equivalent  quanti- 
ties could  be  used,  the  writer  believes  that  no  amount  of 
cooking  would  give  the  sensitive  condition.  Too  large  an 
excess,  on  the  contrary,  tends  to  form  fog,  which  is  not  to 
be  afterwards  got  rid  of  by  the  use  of  bichromate,  but 
which  is  more  liable  to  occur  with  alkaline  pyrogallic 
developer  than  with  ferrous  oxalate.” 

Practically  we  have  proved  that  by  increasing  the  pro- 
portion of  soluble  bromide  to  silver  nitrate  a great  increase 
of  sensitiveness  is  brought  about.  We  are  rather  inclined 
to  think  that  this  is  due  to  the  fact  that  when  the  excess 
is  slight,  the  water  alone  plays  the  part  of  the  solvent  of 
the  silver  bromide,  and  re-precipitates  it  in  not  the 
most  sensitive  form ; whereas,  when  precipitated  from 
water  containing  a large  excess  of  bromide,  the  molecular 
state  is  the  orange  state,  the  boiling,  of  course,  subse- 
quently coagulating  these  molecules  into  particles.  It 
will  be  noticed  that  ammonia  has  the  same  effect  when 
applied  to  a cool  solution,  and  this  we  lay  to  the  same 
cause.  It  is  very  doubtful,  theoretically,  if  an  emulsion 
prepared  in  a cool  state  can  ever  be  as  uniformly  sensitive 
as  one  which  is  prepared  by  the  aid  of  heat,  since  the 
molecular  aggregations  can  scarcely  be  as  homogeneous 


118  SENSITIVENESS  IN  GELATINE  EMULSION. 

as  when  they  are  subjected  to  a certain  amount  of  friction 
to  render  them  so.  In  our  own  experience  we  have  never 
met  with  an  ammonia  prepared  emulsion  which  could  be 
as  rapid  as  one  can  be  prepared  by  boiling. 

It  might  be  supposed  that  a perfectly  neutral  state  or 
an  alkaline  state  of  the  emulsion  should  be  conducive  to 
sensitiveness,  and  seeing  the  use  made  of  ammonia,  there 
is,  at  first  sight,  much  in  it.  Dr.  Vogel,  however,  has,  by 
the  production  of  an  acid  emulsion  (which  he  classes  as 
sensitive  as  ordinary  gelatine  plates),  proved  that  such  is 
not  the  case.  The  production  of  this  emulsion,  one  solvent 
of  which  is  acetic  acid,  and  in  which  silver  bromide  is  not 
soluble,  is  most  valuable  in  a theoretical  point  of  view 
(always  supposing  that  no  material  loss  of  sensitiveness 
is  produced  by  it)  being  one  more  proof  that  the  sensi- 
tiveness is  due  wholly  to  a physical  change,  and  not  to  a 
chemical  change  in  the  silver  bromide. 

There  is  another  fact  of  especial  interest,  which  is,  that 
keeping  an  emulsion  after  preparation  previous  to  coating 
the  plate  is  conducive  to  sensitiveness.  The  following 
table  will  show  the  increase  given  by  keeping.  The 
increase  is  guaged  by  taking  the  first  day’s  sensitiveness 
as  unity.  The  emulsions  were  washed,  and  melted,  and  a 
small  portion  taken  out  of  the  jelly  each  day. 


1st  day. 

2nd  day. 

3rd  day. 

1st  experiment 

1 

1-7 

2*7 

2nd 

1 

2*3 

3-0 

3rd 

1 

2-3 

3*0 

4th 

1 

3-0 

3*0 

5th 

1 

2-3 

3-0 

The  growth  of  sensitiveness  is  here  evident  ,*  keeping 
longer  than  this  appears  to  give  no  practical  increase.  We 
will  try  to  explain  this  phenomenon  theoretically.  The 
editor  of  the  British  Journal  of  Photography  explains  it  on 
the  supposition  that  ammonia  is  formed  in  the  gelatine  by 


SENSITIVENESS  IN  GELATINE  EMULSION. 


119 


keeping  it,  and  that  this  re-acts  on  the  bromide.  From 
what  we  have  said  before,  this  will  be  seen  not  to  be  our 
view ; the  amount  of  ammonia  formed  would  be  very  small, 
and  as  the  water  is  in  the  jelly,  the  solvent  action  would 
not  come  into  play.  Again,  another  point  is  that  we  have 
found  that  if  the  emulsion  be  slightly  acidified  the  same 
result  is  obtained,  which  is  decidedly  against  the  ammonia 
theory.  Our  own  belief  is  that  silver  bromide,  to  be  in 
the  most  sensitive  state,  must  be  placed  entirely  beyond 
any  state  of  strain.*  It  is  during  boiling  that  this  strained 
state  is  probably  given  to  the  particles  of  silver  bromide, 
and  by  subsequently  keeping  the  emulsion  in  the  state  of 
jelly  this  strain  wears  off,  in  a similar  way  to  that  in  which 
glass  is  annealed  by  being  kept  in  a semi-plastic  state. 
When  the  bromide  is  in  dried  gelatine  it  exists  in  the  same 
state  of  strain  as  that  in  which  it  finds  itself  before  the 
plate  is  dried.  When  emulsion  which  has  not  been  kept  is 
spread  on  a plate,  and  one  part  rapidly  dried,  and  the  other 
more  slowly,  it  will  be  found  that  the  part  most  rapidly 
dried  is  less  sensitive  than  the  part  more  slowly  dried.  In 
the  one  case  the  strain  is  taken  off,  and  in  the  other  it  is 
not.  In  the  case  of  an  emulsion  kept  two  or  three  days, 
the  difference  in  sensitiveness  of  the  slow  and  quick  drying 
portions  of  the  plate  is  not  apparent.  Another  cause  of 
apparent  diminution  in  sensitiveness  is  the  use  of  too  hard 
a description  of  gelatine,  and  also  the  use  of  too  small  a 
quantity  of  water  with  it.  The  greatest  part  of  the  sensi- 
tiveness is  present,  but  it  cannot  be  developed.  The  dimi- 
nution of  sensitiveness  is  here  also  probably  due  to  the 
strain  on  the  bromide.  We  made  some  interesting  experi- 
ments regarding  this.  We  had  some  plates,  the  emulsion 
for  which  was  prepared  in  a very  small  quantity  of  water, 
and  the  gelatine  was  very  hard.  Half  of  some  plates  were 


* We  would  invite  a comparison  of  the  effect  of  light  on  silver  chloride 
in  the  crystalline  state  as  produced  by  fusion,  and  in  the  powder  state ; 
even  when  prepared  with  an  excess  of  chloride,  the  latter  will  darken, 
whereas  the  former  remains  nearly  unchanged. 


120 


SENSITIVENESS  IN  GELATINE  EMULSION. 


immersed  in  water  for  half  an  hour,  and  half  of  others  in  a 
mixture  of  1 dr.  of  glycerine  to  half  a pint  of  water  for  the 
same  time.  The  plates  were  then  dried,  and  exposed. 
Those  portions  of  the  plate  which  had  been  wetted  with 
glycerine  and  water  developed  out  with  proper  density ; 
the  difference  with  those  wetted  with  water  alone  was 
not  so  marked  ; the  other  portions  lacked  vigour,  and  were 
apparently  insensitive.  To  prove  whether  the  sensitive- 
ness had  altered  by  the  wetting,  plates  were  exposed,  then 
half  of  them  wetted,  dried  again,  and  then  developed. 
There  was  nearly  the  same  result  as  before.  It  will  be 
seen,  then,  that  to  get  a proper  amount  of  density  and 
sensitiveness  the  gelatine  in  the  emulsion  before  coating 
the  plates  should  have  a liberal  supply  of  water  with  it. 
Various  other  experiments  have  been  made,  all  tending 
to  prove  that  if  great  sensitiveness  is  required,  the  gela- 
tine should  be  as  soft  as  is  consistent  with  safety. 

Another  j)oint  which  is  conducive  to  sensitiveness 
should  be  attended  to.  If  the  solution  in  which  the 
silver  bromide  is  boiled  is  very  viscous,  the  modification 
will  not  take  place  with  any  degree  of  rapidity ; on  the 
other  hand,  fog  is  induced  by  having  the  gelatine  too 
dilute,  since  the  particles  are  built  up  too  coarsely.  Even 
with  the  ammonia  process,  the  same  holds  good,  for  if  an 
emulsion  be  formed  in  cold  solutions,  according  to 
Eder’s  plan,  with  the  minimum  amount  of  gelatine,  it 
will  be  more  sensitive  by  many  degrees  than  if  mixed 
warm  with  the  full  amount  of  gelatine,  and  digested  after- 
wards for  an  hour. 


CHAPTER  XXIY. 


SILVER  IODIDE  AND  CHLORIDE  IN  EMULSIONS. 


There  has  been  some  dispute  regarding  the  advantage  of 
the  use  of  silver  iodide  in  emulsions,  and  we  will  endeavour 
to  put  the  matter  before  our  readers  without  bias.  The 
introduction  of  iodide  in  gelatine  emulsions  was  first  gene- 
rally brought  to  the  knowledge  of  the  photographic  world 
in  a paper  read  before  the  Photographic  Society  of  Great 
Britain,  from  which  we  quote  some  remarks  we  then  made. 

u What  can  be  more  miserable  than  to  go  into  a * gela- 
tine’ man’s  developing  room,  and  see  how  he  fumbles 
about  for  this  thing  and  that,  and  then  finally  develops 
his  plate  almost  by  a tour  de  force  ? I hope  to  show  you 
how  that  can  be  avoided  by  a very  simple  means,  and  I 
do  so  with  the  more  confidence  as  a portion  of  my  experi- 
ments have  been  confirmed  by  a no  unworthy  labourer  in 
the  same  field,  Mr.  W.  England.  The  modification  is 
simplicity  itself.  Bromide  of  silver  is  sensitive  well  into 
the  red  of  the  spectrum,  as  is  well  known,  whilst  bromo- 
iodide  of  silver  is  not. 

u A year  ago  I verbally  mentioned  to  a well-known  gela- 
tine plate  preparer  that  a modicum  of  iodide  of  silver  in 
the  emulsion  took  off  the  great  sensitiveness  to  the  yellow 
and  red  rays  ; and  some  six  months  ago,  in  a letter  I 
wrote  to  the  Belgian  Photographic  Society,  I described 


122 


IODIDE  AND  CHLOKIDE  IN  EMULSIONS. 


certain  experiments  therewith.  Since  that  time,  at  my 
leisure,  I have  worked  at  the  process  with  very  definite 
ideas  of  what  I required,  and  having  found  the  means  ©f 
arriving  at  my  requirements,  I offer  the  results  of  experi- 
ment to  the  Society.  I am  in  a position  to  say  that  an 
emulsion  of  silver  bromo-iodide  can  he  made  just  as 
sensitive  as  the  emulsion  silver  bromide,  as  regards  the 
ordinary  so-called  actinic  rays,  and  can  be  prepared  so  as 
to  be  perfectly  unacted  upon  by  the  orange  or  red  rays, 
which  is  a step  in  the  right  direction,  according  to  my 
way  of  thinking.  If,  instead  of  dissolving  soluble  bromide 
in  the  gelatine  previous  to  precipitating  with  the  silver 
nitrate,  l-6th  part  of  the  quantity  of  soluble  iodide  be 
added,  the  rays  which  affect  the  resulting  washed  emulsion 
are  nearly  those  which  affect  a wet  plate  ; if  l-12th  part 
be  used,  the  compound  is  sensitive  well  into  the  yellow ; 
and  if  l-24th  be  used,  the  emulsion  is  slightly  sensitive 
to  orange,  and  a very  little  into  the  red.  To  those  who 
use  the  spectroscope  one  may  speak  more  definitely.  The 
first  is  sensitive  to  the  rays  above  E,  the  second  to  the 
rays  above  D,  and  the  last  to  the  rays  above  B,  or  there- 
abouts (see  page  3). 

“ Now  about  sensitiveness.  If  such  salts  be  emulsified 
with  (say)  l-6th  to  l-4th  the  amount  of  gelatine  to  be 
finally  used,  and  then  be  boiled  for  equal  times , the  result- 
ing emulsions  will  be  equally  sensitive*  if  kept  a couple  of 
days,  and  in  the  first  case  the  development  can  take  place 
in  a room  in  which  the  ordinary  wet  process  is  worked, 
always  supposing  that  the  glass,  or  covering  of  the  window, 
really  admits  only  orange  light.  With  the  last,  two  pro- 
portions— ruby  and  orange  glass  combined — are  perfect 
protections  during  development,  which  is  more  than  can  be 
said  when  silver  bromide  alone  is  used.  It  is  only  recently 
that  I have  been  undertaking  comparative  experiments, 


* This  is  important,  because  at  first  the  pure  bromide  emulsion  without 
the  iodide  will  have  the  advantage  which  it  more  than  loses  after  keeping. 


IODIDE  AND  CHLORIDE  IN  EMULSIONS. 


123 


and  every  emulsion  made  is  actually  tried  in  the  photo- 
spectroscope, so  that  there  can  be  no  doubt  as  to  what  rays 
the  substance  experimented  upon  is  sensitive.  There  is 
another  great  advantage  in  the  use  of  iodide  even  in  smaller 
proportions,  and  that  is  the  great  clearness  of  the  shadows 
which  is  often  wanting  in  a gelatine  plate.  It  happened 
when  I was  in  the  midst  of  my  most  recent  researches  in 
this  matter  that  I visited  Mr.  England  for  the  purpose  of 
comparing  some  plates  with  his,  and  I found  that  he  also 
had  been  experimenting  in  the  same  direction,  and  had 
arrived  at  the  same  conclusion  as  myself  regarding  the 
sensitiveness  of  the  bromo-iodide  emulsion,  and  also  its 
beautiful  clearness.” 

Col.  Wortley  and  Mr.  Dawson  have  stated  that  in  their 
hands  the  plates  prepared  with  iodide  do  not  keep,*  and 
that  they  are  slower  than  when  prepared  without  it. 
There  have  again  been  others  who  hold  contrary  views, 
amongst  whom  we  may  name  Mr.  England  and  Mr.  W.  B. 
Bolton.  Dr.  Eder  has  expressed  himself  against  the  use 
of  iodide  and  chloride,  in  the  following  terms  : — 

“ I do  not  at  all  see  the  use  of  employing  iodide  of 
silver  in  gelatino- bromide.  I find  that  iodide  is  always 
much  less  sensitive  than  bromide.  Bolton,  Davanne, 
Vogel,  Stillman,  and  others,  have  shown  that  iodide  of 
silver  with  alkaline  development  is  scarcely  at  all  sensi- 
tive. So  in  gelatino-bromide  of  silver,  it  dimininshes  the 
sensitiveness.  If  to  gelatino-bromide  be  added  a quarter 
to  a half  of  iodide  of  silver,  the  plates  in  studio  work 
become  much  less  sensitive,  and  the  negatives  are  feebler 
than  with  pure  bromide  of  silver.  Even  the  addition  of 
one-twelfth  of  iodide  diminishes  considerably  the  sensi- 
tiveness of  an  emulsion.  An  emulsion  of  iodo-bromide 


* Mr.  Dawson  has  quite  recently  told  us  that  this  is  due  to  hygroscopic 
conditions,  the  failure  keeping  pace  with.,  the  amount  of  iodide.  What  is 
the  connection  between  silver  iodide  and  the  hygroscopic  tendency  of  the 
film,  it  is  hard  to  see  theoretically.  We  have  never  found  it  out  thus 
ourselves. 


124 


IODIDE  AND  CHLORIDE  IN  EMULSIONS. 


of  silver  with  one-twelfth  of  iodide  boiled  for  half-an- 
hour  is  not  much  more  rapid  than  an  insensitive  emulsion 
of  simple  bromide  of  silver  unmodified  and  scarcely  boiled. 
Moreover,  those  plates  develop  more  slowly.  The 
advantage  they  possess  in  giving  clearness  in  the  shadows, 
and  of  being  capable  of  development  in  a well-lighted 
dark  room,  does  not  compensate  sufficiently,  in  my 
opinion,  for  the  loss  of  sensitiveness.  And  I hold  as  an 
enormous  advantage  the  great  sensitiveness  of  pure  bro- 
mide of  silver  to  different  colours — an  advantage  which 
should  never  be  given  up.  The  ideal  of  a photographic 
plate  would  be  to  have  the  greatest  possible  sensitiveness 
towards  the  red  extremity  of  the  spectrum  (red,  yellow, 
and  green).*  This  plate  would  give  the  effects  of  natural 
light,  and  the  play  of  light  and  shade  would  be  rendered 
in  the  photograph  much  as  it  appears  to  the  human  eye. 
Of  all  the  productions  at  present  known,  bromide  of  silver, 
pure  and  modified,  most  nearly  approaches  this  ideal. 

u I consider  as  even  more  unfavourable  than  the  addi- 
tion of  iodide  of  silver,  the  use  of  chloro-bromide  of  silver. 
We  see  springing  up  on  all  sides  recipes  for  chloro-iodo- 
bromide  emulsions.  I would  strongly  protest  against  all 
these  absurdities.  Chloride  of  silver  is  reduced  with 
infinitely  more  ease  and  rapidity  than  bromide.  It  is  also 
tolerably  sensitive  to  light,  and  receives  equally  the  latent 
image  during  the  time  of  exposure  necessary  to  bromide 
offsilver.  The  strong  developer  necessary  for  bromide  is, 
however,  much  too  forcible  for  chloride.  Chloride  of 
silver  blackens  completely  throughout  before  the  bromide 
is  reduced  in  the  lights.  Hence  there  is  always  fog  in 
chloro-bromide  plates,  unless  there  be  added  to  the 
developer  sufficient  bromide  of  potassium  to  transform  to 


# We  may  remark,  regarding  this,  that  the  sensitiveness  of  silver  bromide 
in  the  state  in  which  it  is  found  in  the  gelatine  emulsion  is  vastly  different 
for  the  red,  yellow,  and  blue  rays.  If  the  first  be  said  to  have  a sensi- 
tiveness of  1,  the  yellow  may  be  said  to  have  about  5,  and  the  blue  at 
least  100.  We  are  at  present  thus  very  far  from  an  ideal  plate. 


IODIDE  AND  CHLORIDE  IN  EMULSIONS. 


125 


bromide  of  silver  all  the  chloride,  [and  thus  cause  an 
irregular  reduction. 

u First,  as  to  the  iodide.  We  must  look  on  it  in  two 
aspects  : one  in  which  it  alters  the  physical  aspect  of  the 
film  in  which  it  is  used  ; and  the  second,  in  regard  to  the 
chemical  aspect.  Now,  where  alkaline  development  is 
used,  the  iodide  is  so  much  inert  salt  in  the  film.  Supposing 
(as  we  always  do  suppose,  and  most  rigidly  cling  to)  that 
the  iodide,  bromide,  and  chloride  of  silver  are  reduced  by 
light  to  the  form  of  a sub-salt  of  silver,  it  may  be  well  to 
glance  briefly  at  the  action  that  iodide  may  have.” 

Supposing  iodine  is  set  free  after  exposure,  what 
becomes  of  it  ? and  also  the  bromine,  what  becomes  of  it  ? 
Iodides  of  the  alkalies  will  displace  bromine  in  the  bro- 
mides of  silver,  as  we  are  all  aware,  but  iodine  will  not 
displace  bromine,  but,  on  the  contrary,  bromine  will  dis- 
place iodine  apparently  till  they  are  in  the  proportion  of 
their  molecular  weight.  If,  then,  we  have  bromine  and 
iodine  liberated  by  the  action  of  light,  the  bromine  will 
attack  the  particles  of  iodide  in  its  immediate  neighbour- 
hood, and  we  have  a double  quantity  of  iodine  set  free. 
In  other  words,  we  have  all  iodine  liberated  instead  of 
bromine.  At  first  sight  it  might  seem  that  double  work 
was  here  done,  so  that  there  was  a loss  of  energy ; but 
a little  consideration  will  show  that  this  is  not  the  case. 
The  only  loss  of  energy  which  can  be  taken  into  account 
is  the  difference  of  the  affinities  of  gelatine  for  iodine,  and 
of  gelatine  for  bromine.  Iodine  has  a greater  affinity  for 
gelatine  than  has  bromine,  so  that  as  regards  loss  of 
energy,  and  consequent  sensitiveness  in  this  repect,  the 
mixture  of  iodide  has  the  advantage.  It  remains,  how- 
ever, to  consider,  when  we  may  expect  that  a mixture  of 
iodide  with  bromide  will  act  prejudicially.  This  will  be 
when  the  number  of  particles  of  iodide  acted  upon  by 
light  (and  which  are  undevelopable,  and  consequently  a 
cause  of  diminution  in  sensitiveness)  bear  such  a propor- 
tion to  the  particles  of  bromide  that  the  increased  affinity 


IODIDE  AND  CHLORIDE  IN  EMULSIONS. 


126 


of  iodine  over  bromine  for  gelatine  is  more  than  counter- 
balanced. The  exact  theoretical  figures  are  very  difficult 
to  give,  but  we  should  say  that  if  a surface  contains  l-10th 
of  iodide  to  1 of  bromide,  the  sensitiveness  would  remain 
the  same  as  when  none  was  used ; whilst  with  l-20th 
there  should  be  a small  increase.  Now  as  regards  the 
physical  state  of  the  silver  : we  have  shown  that  the 
addition  of  iodide  acts  as  a restrainer  to  fog,  and  is,  of 
course,  not  the  least  a destroyer  of  the  image.  In  other 
words,  it  means  that  you  can  use  more  ammonia  and  less 
bromide  when  developing  it.  For  instance,  in  the  albumen 
beer  process  with  the  bath*  the  image  is  developed  with 
strong  ammonia  and  pvrogallic  acid,  and  with  no  restrainer 
whatever  beyond  the  physical  restraint  caused  by  the 
albumen  ana  the  iodide.  It  may  be  said  the  albumen 
alone  played  the  part ; but  that  is  not  the  case  ; if  with  a 
collodio-bromide  emulsion  you  use  the  same  preservative 
in  a similar  manner,  the  use  of  a bromide  in  the  developer 
becomes  a necessity." 

As  to  the  use  of  chloride,  there  is  much  to  be  said  for 
a moderate  use  of  it.  Development  might  be  modified  to 
suit  it.  We  have  found  that  using  half  bromide  and 
half  chloride  a sensitive  and  beautiful  picture  will  result 
when  using  the  ferrous-citro-oxalate  developer.  There 
is  no  doubt,  from  our  experiments,  that  silver  chloride 
aids  density,  and  this  itself  is  a great  advantage.  We 
know  several  advanced  workers  who  add  all  three  haloids 
(iodide,  bromide,  and  chloride)  with  the  best  possible 
results.  Another  use  of  chloride,  as  far  as  we  know,  is  to 
allow  a full  dose  of  silver  to  be  used  to  convert  all  the 
bromide  present  in  emulsion  without  jeopardizing  it  by  an 
introduction  of  free  silver.  Bromine  displaces  chlorine  in 
the  chloride  of  silver,  when  the  bromine  is  in  the  form  of 
a bromide  of  the  alkalies,  hence  the  addition  of  a certain 
amount  of  chloride  is  useful,  even  with  ordinary  develop- 


* See 


‘ Instruction  in  Photography.' 


IODIDE  AND  CHLORIDE  IN  EMULSIONS. 


127 


ment.  It  may  be  objected  that  by  this  procedure  tbe 
bromide  is  not  boiled  in  a medium  which  has  solvent 
powers.  This  is  not  the  case,  however,  as  the  bromide  is 
soluble  to  a certain  extent  in  the  soluble  chloride.  It  is 
very  easy  to  mix  a chloride  emulsion  with  a bromide 
emulsion  after  washing,  and  for  some  purposes  this  is  a 
good  plan. 


CHAPTER  XXY. 


COMPARISON  OF  THE  AMMONIA  PROCESSES 
WITH  THE  BOILING  PROCESS. 


We  will  now  pass  on  to  describe  comparative  results  of 
Dr.  Eder’s  methods  of  emulsification  by  the  use  of 
ammonia,  and  of  the  boiling  method. 

Two  emulsions  were  made  according  to  Eder’s  first 
formula ; the  second  containing  about  10  per  cent,  of 
potassium  iodide,  and  called  I.  and  II.  Two  emulsions 
were  made  according  to  Eder’s  second  formula,  one  also 
containing  about  10  per  cent,  of  potassium  iodide,  and 
called  III.  and  IV. 

A variety  of  emulsions  were  made  and  tested  one 
against  the  other  in  many  ways.  We  give,  in  a tabular 
form,  some  of  the  results  : — 


No.  I. — Potassium  bromide  ... 

Swinburne’s  No.  2 isinglass 
Nelson’s  No.  1 photo,  gelatine 
Water 

Silver  nitrate 

Water  


93  grains 
30  „ 
120  „ 

2i  oz. 
115  grains 
2 i oz. 


COMPARISON  OF  PROCESSES. 


129 


— Potassium  bromide  ... 

...  93  grains 

Potassium  iodide 

...  10  „ 

Nelson’s  No.  1 photo,  gelatine 

...  120  „ 

Swinburne’s  No.  2 isinglass 

...  30  „ 

Water 

...  2j  oz. 

Silver  nitrate 

...  127  grains 

Water 

2i  oz. 

These  had  been  made  according  to  Dr.  Eder’s  formula, 
with  ammonia. 

Nos.  V,  VI , were  made  with  the  above  formulae,  but  boiled 
with  15  grains  of  gelatine  for  half-an-hour ; 105  grains  of 
No.  1 photographic  gelatine  and  30  grains  of  Swinburne’s 
isinglass  were  dissolved  in  2 ounces  of  water,  and  added 
to  them.  They  were  each  divided  into  two  parts,  and  one- 
half  of  each  was  digested  with  1 drachm  of  strong 
ammonia,  as  in  experiments  III  and  IV.  The  other  halves 
were  washed  without  having  been  digested  with  ammonia. 
All  were  allowed  to  set,  and  then  washed  as  usual.  Those 
portions  of  V and  VI  of  the  emulsions  treated  with 
ammonia  we  will  call  Nos.  VII  and  VIII  respectively. 

Plates  were  coated  with  all  the  emulsions  : 1st,  on  the 
same  day  on  which  the  washing  was  complete  ; 2nd,  on 
the  day  after,  and  then  tested  one  against  another.  It 
may  be  convenient  to  call  the  greatest  sensitiveness  10, 


and  to  show  the  others 
following  results : — 

5 by  lower  numbers. 

We  find  the 

No.  VI 

...  2nd  day  ... 

...  10 

No.  VIII  ... 

...  2nd  day 

...  10 

No.  V 

...  2nd  day  ... 

...  9 

No.  VII  ... 

...  2nd  day  ... 

...  9 

No.  VII  ... 

...  1st  day 

...  8 

No.  VIII  ... 

...  1st  day 

...  7 

No.  IV 

...  2nd  day  ... 

...  6 

No.  Ill 

...  2nd  day  ... 

...  6 

No.  IV 

1st  day 

...  5 

No.  Ill 

...  1st  day 

K 

...  5 

130 


COMPARISON  OF  PROCESSES. 


No.  VI 

...  ...  1st  day 

...  5 

No.  V 

...  ...  1st  day 

...  5 

No.  I 

...  ...  2nd  day  ... 

...  4* 

No.  II 

...  ...  2nd  day  ... 

...  4 

No.  I 

s...  ...  1st  day 

...  3i 

No.  II 

...  o..  1st  day 

...  3 

may  be 

convenient  to  remember 

that  the  odd 

numbers  contain  bromide  alone,  and  the  even  ones  iodide 
with  the  bromide. 

It  will  be  seen,  when  boiling  with  a small  quantity  of 
gelatine  (Nos.  V,  VI,  VII,  and  VIII),  that  at  the  second 
day  the  plates  containing  iodide  (VI  and  VIII)  have  a 
little  advantage  over  those  which  contain  bromide  alone, 
and  that  the  digestion  with  ammonia  (VIII)  gives  no 
increase  in  sensitiveness.  The  same  is  apparent  with  VII 
and  V ; the  digestion  with  ammonia  does  not  increase  the 
sensitiveness  with  pure  bromide.  The  first  day’s  plates 
(VI  and  VIII)  with  the  iodide  are  in  every  way  behind  the 
second  day’s  plates  with  the  bromide  alone  ; but  evidently 
digestion  with  ammonia  answers  partly  the  same  end  as 
keeping  the  emulsion.  The  same  applies  also  to  Nos.  I 
and  II.  Boiling  with  a small  amount  of  gelatine,  then,  in 
every  case,  is  better  than  boiling  with  a full  quantity  of 
gelatine,  and  then  digesting  with  ammonia ; but  this 
plan  is  far  better  than  digesting  with  ammonia  alone. 
These  formulas  are  comparative  ones,  since  they  all 
contain  eventually  the  same  amount  of  bromide  of  silver, 
and  the  same  amount  of  gelatine. 

As  regards  development,  the  plates  containing  the 
iodide  were  a little  slower  in  coming  out ; but,  on  the 
other  hand,  they  were  certainly  much  brighter  and 
cleaner. 

To  test  the  value  of  the  iodide  further,  the  same 
formula  as  Nos.  Ill  and  IV  were  used,  and  the  emulsions 
brought  to  the  boiling-point  when  the  ammonia  was 
present.  No.  Ill  fogged  • No.  IV  remained  quite  bright. 


COMPARISON  OF  PROCESSES. 


131 


The  ammonia  undoubtedly  makes  plates  much  more  rapid 
than  when  no  boiling  is  attempted ; the  sensitiveness  in 
which  case  might,  perhaps,  be  represented  as  1,  but  it 
by  no  means  gives  the  most  rapid  kind  of  plate.  We 
think  for  comparatively  slow  plates,  where  good  density 
is  required,  Formula  No.  II  is  excellent  in  everyway; 
and  if  anyone  has  a prejudice  against  iodide,  let  him  use 
No.  I. 

It  will  thus  be  seen  that  we  hold  to  introduction  of 
iodide  into  an  emulsion ; except  for  experimental  pur- 
poses we  never  omit  it,  believing  it  to  be  a sheet-anchor 
for  obtaining  good  and  unfogged  pictures.  We  are  aware 
that  several  commercial  makers  of  plates  which  have  a 
great  name  in  the  market  use  the  iodide,  and  if  those  who 
condemn  it  would  but  give  it  a fair  and  unprejudiced 
trial,  we  should  have  no  fear  of  making  converts  of  them 
to  its  introduction. 


CHAPTER  XXVI. 


GELATINE. 

In  gelatine  emulsions  one  of  the  most  prominent  features 
is  the  gelatine,  and  it  is  by  no  means  unimportant  what 
kind  is  selected.  Dr.  Eder  has  made  long  and  exhaustive 
researches  on  various  qualities  of  gelatine,  and  Mr.  T.  F. 
Elsden  has  also  thrown  light  upon  its  variability  in  an 
article  in  the  Year-Book  for  1881,  and  we  cannot  do 
better  than  quote  some  of  their  conclusions.  Gelatine  is 
compound  of  glutin  and  chondrin.  The  latter  is  dis- 
tinguished from  the  former  by  its  precipitation  from  an 
aqueous  solution  by  acetic  acid,  and  its  insolubility  in  an 
excess  of  this  reagent.  Acetate  of  lead,  alum,  and  sul- 
phates of  iron,  aluminium,  and  copper  also  precipitate  it ; 
but  not  glutin.  Mr.  Elsden  also  remarks  that  a con- 
venient test  for  the  presence  of  much  chondrin  in  gelatine 
is  to  add  a concentrated  solution  of  chrome  alum  to  a 
solution  of  50  grains  of  gelatine  in  1 ounce  of  water.  If 
chondrin  be  present  in  excess,  the  gelatine  will  set  whilst 
hot.  Mr.  Elsden  further  says  : — Remembering  that  gela- 
tine is  a mixture  of  two  substances  of  different  composi- 
tion and  properties,  it  must  be  expected  to  find  great 
variation  in  the  behaviour  of  commercial  samples.  Most 
photographic  gelatines,  however,  consist  chiefly  of  glutin, 
and  their  general  character  is  not,  therefore,  affected  to  so 
great  an  extent  by  the  small  quantity  of  chondrin  usually 
present  in  addition. 

Gelatine  is  extremely  hygroscopic,  and  contains,  at 


GELATINE. 


133 


ordinary  temperatures,  from  fifteen  to  twenty  per  cent, 
of  water.  In  cold  water  it  swells  up,  and  absorbs  from 
five  to  ten  times  its  weight  of  water  ; good  gelatine  will 
absorb  enough  cold  water  to  dissolve  it,  if  the  temperature 
is  raised  above  90°  F.  Very  weak  solutions  of  gelatine 
will  solidify  to  a jelly  when  cold,  sometimes  when  only 
one  per  cent,  is  present ; but  long  boiling  destroys,  to  a 
great  extent,  this  power  of  setting. 

Gelatine  will  keep  indefinitely  in  a dry  state  ; but  in 
contact  with  water  it  soon  putrefies,  becoming  first  acid, 
and  then  strongly  alkaline,  and  giving  off  ammonia  ; at  a 
temperature  of  90°  F.,  decomposition  will  often  begin  in 
twenty-four  hours.  Hence  it  is  evident  that  long  boiling, 
besides  destroying  its  power  of  setting,  also  tends  to  pro- 
duce decomposition  of  gelatine. 

Alum,  alcohol,  carbolic  acid,  salicylic  acid,  glycerine, 
fuchsin,  hydrate  of  chloral,  thymol,  and  salts  of  zinc  act 
as  antiseptics,  preventing  the  decomposition  of  gelatine, 
even  in  small  quantities.  If  glycerine  be  used,  however, 
it  must  be  added  in  rather  large  quantities.  Alcohol  and 
carbolic  acid,  in  large  quantities,  precipitate  gelatine  from 
solution  in  water. 

Acetic  acid,  hydrochloric  acid,  sulphuric  acid,  and 
oxalic  acid  dissolve  gelatine  even  in  the  cold. 

Acetic  acid  dissolves  gelatine  with  great  facility,  whilst 
ammonia  acts  as  a weak  solvent. 

Sugar  promotes  the  solubility  of  gelatine,  whilst  gum, 
in  the  presence  of  acetic  acid,  renders  gelatine  less  soluble, 
owing  to  the  formation  of  a compound  of  glutin  with 
arabic  acid. 

Silver  nitrate,  exposed  to  sunlight,  in  contact  with 
gelatine,  causes  a red  discolouration,  due  to  the  combina- 
tion of  organic  matter  with  a sub-oxide  of  silver. 

Chrome  alum  renders  gelatine  insoluble  ; but  long  boil- 
ing and  hot  dilute  acids,  potash,  potassium  permanganate, 
are  able  to  dissolve  the  mixture.  Alum  raises  the  melt- 
ing point,  but  does  not  render  it  insoluble 


134 


GELATINE. 


The  quality  of  gelatine  may  be  tested  in  several  ways. 
Dr.  Eder,  amongst  other  tests,  recommends  that  the  gela- 
tine be  incinerated,  and  the  ash  weighed,  and  he  says  that 
this  varies  from  J per  cent,  in  good  samples  to  5 per  cent, 
in  inferior  kinds  of  gelatine,  and  to  1 0 per  cent,  if  adulte- 
rated with  alum.  Our  own  researches  in  this  matter  give 
a greater  margin  for  good  gelatines,  2 ’5  per  cent,  being  the 
ash  of  a certain  gelatine  which  is  excellent.  We  detail 
some  results  in  the  table  below.  Another  test  which 
should  be  applied  is  the  amount  of  water  it  can  absorb. 
Good  gelatine  should  absorb  five  to  ten  times  its  weight  of 
water.  A very  simple  way  ot  testing  is  to  measure  out 
(say)  2 ounces  of  water,  and  soak  50  grains  of  the  gelatine 
in  it  for  some  hours  until  it  is  thoroughly  swelled.  The 
water  not  taken  up  should  then  be  poured  off  into  a 
measure,  the  gelatine  being  very  gently  pressed  against 
fhe  side  of  the  vessel  in  which  it  was  allowed  to  swell. 
The  amount  taken  up  is,  of  course,  the  difference  between 
the  2 ounces  and  the  amount  returned  to  the  measure.  A 
more  scientific  method  is  to  allow  the  gelatine  to  take  up 
as  much  water  as  it  can  at  a fixed  temperature,  drain  it, 
and  surface  dry  it  on  blotting-paper,  and  then  weigh  it. 
This  is  a more  tedious  method  than  that  given  above. 

Water  absorbed 

Name  of  Gelatine  Ash,  per  cent.  by  50  grains. 

Coignet’s  gold  label  gelatine  ...  1 nearly  ...  7 drachms 
„ special  gelatine  ...  1 
Nelson’s  No.  1 photographic  ...  2 
„ opaque  ...  ...  2 

„ amber...  ...  ...  1 

Ordinary  French  (not  branded)  2 
Swinburne’s  No.  2 patent  ising- 
glass  ...  ...  ...  1 

Cox’s  gelatine  in  packets  ...  1 

Russian  isinglass  ...  ...  1 

Gelatine  supplied  through  Mr. 

Henderson...  ...  ...  2 

The  Swiss  gelatine  supplied 
through  Houghton  ...  2 


?? 

... 

i 

... 

?? 

J? 

... 

8 

r> 

... 

4 

?? 

... 

o 

J? 

)? 

... 

5} 

?? 

43 

?? 

... 

?? 

5? 

... 

9JL 

r> 

?? 

... 

8 

... 

5 

GELATINE. 


135 


The  next  test  is  that  of  solubility.  A gelatine  which  by 
itself  is  soluble  at  a low  temperature  is  unfitted  for  gela- 
tine emulsions,  particularly  if  the  temperature  at  which  it 
is  prepared  is  at  all  high,  since  it  would  then  not  set. 
Take,  as  an  example  of  this,  Nelson’s  No.  1 gelatine.  In 
warm  weather  it  will  dissolve  in  the  water  at  the  tempera- 
ture of  the  room  in  which  it  is  soaked.  Take  Coignet’s 
gold  label  as  the  other  extreme,  and  it  will  be  fonnd  not 
to  melt  till  the  vessel  has  been  plunged  into  water  about 
110°.  As  might  be  expected,  as  regards  setting,  these 
two  gelatines  are  the  most  opposite.  At  a temperature  of 
about  75°,  No.  1 will  scarcely  set  at  all,  whereas  Coignet’s 
will  set  in  a short  time. 

An  important  test  is  for  acidity  or  alkalinity.  For  our 
* own  part  we  strongly  recommend  a gelatine  which  is 
slightly  acid  where  an  emulsion  is  to  be  boiled,  and  if  not 
in  this  state,  we  acidify  the  gelatine  solution.  When  the 
ammonia  process  is  used,  the  condition  of  the  gelatine 
does  not  matter  so  much.  In  some  gelatines,  the  acidity 
(due  to  the  hydrochloric  acid  used  in  its  manufacture) 
can  be  tasted  by  applying  a piece  to  the  tongue.  A 
hard  gelatine  can  be  at  once  identified  when  it  is  set 
after  dissolving  in  the  water,  which  it  will  absorb.  Any 
exact  determination  bv  applying  weight  to  see  where 
crushing  begins  is  misleading,  unless  the  temperature 
is  uniform  during  all  experiments. 

We  would  here  remark  that  gelatine  has  an  affinity  for 
iodine,  bromine,  and  chlorine,  with  each  of  which  it  com- 
bines ; hence  it  is  a preservative  in  the  true  sense  of  the 
word. 

The  less  fatty  matter  present  the  better,  since  it  gives 
rise  to  opaque  spots  on  development,  or  else  to  scum- 
markings  on  the  plate.  Where  there  is  fatty  matter  present, 
it  may  be  got  rid  of  by  precipitating  it  in  a fine  stream  in 
alcohol,  or  by  dissolving  it  in  the  quantity  of  water  which 
has  to  be  used,  and  skimming  it ; or  by  making  it  set,  and, 
with  a clean  ivory  knife,  cutting  off  a thin  layer  from  the 
top. 


136 


GELATINE. 


To  select  suitable  gelatine  for  an  emulsion,  we  recom- 
mend that  a small  batch  of  emulsion  be  made  with  the 
specimens  proposed  to  use,  and  that  a few  plates  not 
smaller  than  7 by  5 be  coated  and  tested  before  taking  it 
into  use  for  larger  quantities. 

In  our  own  practice  we  like  to  use  a mixture  of  two 
kinds  of  gelatine — one  hard  and  one  soft,  and  the  propor- 
tions of  these  we  vary  according  to  the  weather.  As  a 
rule,  we  like  1 part  of  hard  to  3 parts  of  solt,  as  it  will 
then  set  with  ease  at  a moderate  temperature,  and  be  hard 
enough  to  resist  the  tendency  to  frill ; and  is  at  the  same 
time  readily  permeable  by  the  developing  solutions. 

One  fact  must  also  be  recollected,  that  frequent  re- 
heating of  gelatine  speedily  detracts  from  its  setting- 
powers,  and  that  if  too  little  water  be  added  to  it  in  mixing, 
the  film  has  a great  tendency  to  become  leathery,  more 
particularly  if  a little  chrome  alum  has  been  added  to  it 
to  prevent  frilling.  A judicious  mixture  of  alcohol  to  a 
gelatine  solution  increases  permeability,  and  should  not 
be  neglected.  The  use  of  a sufficient  quantity  of  water 
is,  however,  the  great  desideratum,  and  should  be  carefully 
attended  to,  the  quantity,  of  course,  depending  on  the 
temperature  at  which  the  plates  have  to  be  prepared ; 
thus,  in  winter,  more  water  should  be  used  than  in  summer. 
A very  horny,  glassy,  film  is  objectionable  in  many  ways, 
and  a matt  surface  for  the  plates  should  be  aimed  at. 
This  depends  almost  entirely  on  the  gelatine  that  is  used, 
unless  it  be  modified  by  additions  such  as  glycerine,  to 
which  we  may  at  once  say  we  object,  on  account  of  its 
affinity  for  water. 


CHAPTER  XXVII. 


GEL  ATINO-BROMC- IODIDE  EMULSION* 

We  propose  to  give  a detailed  account  of  making  an 
emulsion  at  ordinary  temperatures,  say  up  to  65°  Fall., 
which  may  he  taken  as  a pattern  on  which  to  form  others 
by  any  other  formula.  It  will  be  found  to  be  exquisitely 
sensitive  to  the  blue  rays,  and  very  slightly  to  the  yellow, 
which  latter  quality  means  that  the  development  and  pre- 
paration of  the  plates  can  be  conducted  in  a room  with 
any  quantity  of  orange  light.  To  prepare  the  windows 
for  this,  the  ordinary  window  panes  may  be  coated  with 
such  a material  as  Thomas’s  ruby  varnish  paper,  which 
will  be  found  quite  sufficient  protection  ; though  if  direct 
sunlight  beat  on  the  window,  it  is  desirable  to  have  a 
blind  of  orange  paper  or  calico,  which  subdues  the  light, 
since  the  blue  rays  from  a very  strong  light  might  pierce 
the  first  paper  if  there  are  any  deficiencies  in  the  varnish- 
ing. Ruby  glass  and  such  a screen  or  curtain  is  a certain 
protection,  and  is  convenient,  since  there  is  no  danger  of 
any  change  of  colour  in  the  former  through  the  action  of 
light  or  by  any  chemicals  that  may  be  used.  A combina- 
tion of  pot-orange  or  stained  red  glass,  which  admits  about 
the  same  rays,  would  answer  equally  well.  The  dyes  made 
up  in  varnish,  as  given  at  page  30,  may  also  be  sub- 
stituted. The  ordinary  dark-room  windows,  if  covered 


138 


GELATINO-BROMO-IODIDE  EMULSION. 


with  red  tissue  paper  such  as  is  supplied  for  fancy  decora- 
tions, will  render  the  light  safe.  The  reader  must 
remember  that  tricks  cannot  be  played  with  the  light  of 
the  dark-room,  such  as  are  admissible  when  the  com- 
paratively slow  wet  process  is  used.  Thus  he  should  see 
that  no  light  of  the  wrong  colour  penetrates  at  anyplace; 
he  should  pay  particular  attention,  for  instance,  to  the 
chinks  under  the  door,  and  in  the  sashes  of  the  window 
frame.  When  he  has  come  to  the  conclusion  that  no  day- 
light is  entering  his  room,  he  may  think  about  preparing 
the  emulsion.  First  of  all  he  must  make  a few  prepara- 
tions. The  jar  or  bottle  in  which  the  emulsion  has  to  be 
mixed  must  be  scrupulously  clean.  There  should  be  no 
patches  of  old  emulsion  left  on  it.  If  a glazed  jar  be 
used,  it  should  be  seen  that  the  glaze  is  not  cracked  in 
any  way,  since  fog  may  be  expected  if  it  be.  For  dis- 
solving the  gelatine,  &c.,  we  like  to  use  glass  beakers  with 
a lip,  since  they  are  handy  for  pouring.  These  also  must 
be  scrupulously  clean  and  dry.  The  scales  in  which  the 
weighing  has  to  take  place  should  be  examined  for  dirt 
(chemical  or  otherwise),  and  a few  circular  filter  papers 
on  which  to  weigh  the  materials  should  be  at  hand. 
Weighing  should  never  be  done*  without  a filter  paper  of 
equal  size  and  weight  being  placed  in  each  pan  of  the 
scale.  A saucepan  of  hot  water  should  be  ready  in 
which  to  place  the  beakers,  &c.,  in  which  the  different 
materials  have  to  be  dissolved,  and  care  should  be  taken 
that  it  is  not  too  full.  It  need  scarcely  be  said  that  all 
weighing  can  be  done  in  ordinary  light.  To  commence 
operations,  the  following  may  be  weighed  out  separately 
and  placed  on  clean  f paper  after  weighing,  it  being 


* Especially  on  brass  scale  paDS. 

f Any  contamination  by  dirt  of  any  description,  and  particularly  that  to 
be  found  in  a photograph  r’s  work  room,  is  almost  sure  to  spoil  the  emulsion, 
or  at  all  events  its  sensitiveness,  and  to  cause  endless  evils.  Hence  clean 
paper  should  be  used,  and  the  chemicals  should  not  be  left  on  the  benches  or 
table  in  contact  with  the  wood. 


ERRATA. 


At  page  139,  after  the  different  weighings,  it  is  said 
“ Nos.  1 and  2 are  rapidly  covered  with  water.”  It  should 
read  “ Nos.  3,  5 and  6 are  rapidly  covered  with  water.” 
And  in  the  fourth  line  below,  instead  of  “ They  are  then 
dissolved  in  1 dr.  and  1J  ounces  of  water,”  it  should  read 
“Nos.  1 and  2 are  then  dissolved  in  1 dr.  and  1^  ounces 
of  water.” 


GELATINO-BROMO-IODIDE  EMULSION. 


139 


supposed  that  a dozen  or  a few  more  whole-plates  are 
required. 

1.  — Potassium  iodide  ...  ...  10  grains 

2.  — Ammonium  bromide...  ...  140  „ 

3.  — Nelson’s  No.  1 photographic 

gelatine  ...  ...  ...  30  „ 

4.  — Silver  nitrate...  ...  ...  200  ,, 

5.  — Nelson’s  No.  1 photographic 

gelatine  ...  ...  ...  80  „ 

6. — Simeon’s  Swiss  gelatine,  or 

Coignet’s  special  gelatine  ...  80  ,, 

Nos.  1 and  2 are  rapidly  covered  with  water,  shaken  or 
stirred  in  it  a few  seconds,  and  the  water  poured  off  as 
quickly  as  possible.  This  gets  rid  of  any  adherent  dust 
on  them.  They  are  then  dissolved  in  1 dr.  and  1 ounces 
of  water  (ordinary  tap  water  is  good  enough),  respectively, 
and  then  No.  3 is  added  to  No.  2,  and  allowed  to  swell 
in  the  liquid.  It  may  require  a little  coaxing  to  get  it 
beneath  the  surface  of  the  water ; hut  if  a good-sized 
developing  cup  be  used  there  will  not  be  much  difficulty. 
When  swollen,  the  cup  containing  the  salts  and  the  gela- 
tine is  placed  in  boiling  water  for  a few  minutes,  till  the 
latter  is  dissolved  (which  it  will  readily  do  in  a very  short 
time),  and  raised  to  the  temperature  of  about  150°  F.  ; if 
the  gelatine  be  alkaline,  1 drop  of  hydrochloric  acid  may  be 
added  (see  Chap.  XXXIV.)  The  silver  No.  4 meanwhile 
is  also  dissolved  in  ounces  of  water  slightly  warm. 

This  last  may  be  placed  in  a spray  apparatus,  which 
is  made  as  follows  : — Bend  two  thin  glass  tubes  in  a 
common  fish-tail  burner  of  the  shapes  A and  B (fig.  11). 
The  tube  A should  first  of  all  be  drawn  out  so  that  the 
end  is  perfectly  closed ; this  may  be  done  by  the  heat  of 
a Bunsen  burner,  by  holding  the  straight  tube  over  it  at 
about  an  inch  from  the  end,  in  one  hand,  and  at  any  con- 
venient distance  in  the  other,  and,  when  thoroughly 
softened  by  the  heat  at  one  point,  by  simply  pulling  the 


140 


GELATINO-BKOMOIODIDE  EMULSION. 


tube  outwards.  The  glass  collapses,  and  the  short  hit  is 
pulled  off.  A flat  file  is  then  applied  to  the  point,  and 
the  glass  filed  away  till  a very  small  orifice  is  left.  The 
two  tubes  are  then  inserted  in  a cork  which  is  fitted  into 
a test-tube  as  shown.  The  silver  nitrate  is  placed  in  the 


bottom  of  the  tube,  and  a very  fine  spray  of  liquid  can  be 
forced  through  the  orifice  of  A. 

The  solution  of  gelatine  and  bromide  should  be  placed 
in  a glass  beaker  or  a jam-pot,  and  in  the  dark  room  the 
spray  is  blown  on  to  it,  and  the  liquid  stirred,  at  the  same 
time,  with  a clean  glass  rod.  When  the  silver  nitrate  has 
been  added  to  the  bromide  the  iodide  is  dropped  in  with 
stirring,  and  the  remainder  of  the  silver  solution  subse- 
quently added.  This  is  a better  plan  than  adding  it  to  the 
bromide  at  first,  and  depends  for  its  value  on  the  fact  that 
the  iodine  from  the  iodide  will  replace  the  bromine  from 
the  silver  bromide,  soluble  bromide  being  re-formed; 
grains  of  silver  iodide  thus  formed  have  the  same  size  as  the 
bromide  originally  formed.  This  gives  a very  fine  emul- 
sion indeed,  and,  if  correctly  carried  out,  a drop  of  it, 
when  poured  on  a strip  of  glass,  should  show  an  orange- 
yellow  colour  by  transmitted  daylight,  or  a deep  ruby 


GELATINO-BROMO-IODIDE  EMULSION. 


141 


when  a gas  or  candle  flame  is  examined  through  it.  The 
possible  sensitiveness  of  an  emulsion  depends  almost 
entirely  on  the  fineness  of  grain  of  the  bromide  when  first 
formed.  With  a grey  or  blue-tinted  emulsion  extreme 
rapidity  can  never  be  hoped  to  be  attained.  The  emulsion 
should  be  transferred  to  a 20-ounce  bottle*  and  well  shaken 
for  a couple  of  minutes,  after  which  it  is  ready  for  the 
next  operation. 

Other  Methods  of  Mixing. — There  are  other  methods  of 
emulsifying  which  are  given  here.  Mr.  England  finds  that 
if  two  1-drachm  measures  be  filled,  one  with  the  bromide 
solution,  and  the  other  with  the  silver  nitrate  solution,  and 
then  be  poured  into  a bottle  together  and  well  shaken,  and 
this  operation  be  repeated  again  and  again  till  the  two 
solutions  are  exhausted,  he  gets  a perfect  emulsion  with- 
out grain  and  very  smooth.  It  will  be  noticed  that  in 
this  plan  the  silver  and  the  bromide  solutions  are  in 
equal  quantities.  Another  plan,  adopted  by  Mr. 
Warnerke  (whether  it  is  original  with  him  is  not  of  great 
consequence)  is  to  draw  out  two  funnels  to  fine  points, 
and  support  them  on  funnel-holders  over  a jar.  These 
are  filled  with  the  two  solutions,  which  are  allowed  to 
run  into  the  jar,  a stirrer  being  used  to  aid  emulsification  ; 
other  workers  use  the  scent-diffuser,  by  which  to  secure 
fineness  of  grain.  Any  of  these  artifices  may  be  employed. 
A later  plan  which  the  writer  has  adopted,  and  which  is 
very  effective,  is  to  shake  the  gelatine  containing  the  bro- 
mide into  a troth,  and  then  to  add  the  silver  nitrate  little 
by  little.  This  makes  a beautifully  fine  emulsion,  and 
seems  to  be  equivalent  to  immersing  a delicate  film  of  gela- 
tine into  a silver  bath,  when  we  know  that  splendid  films 
are  to  be  obtained,  having  the  very  finest  grain. 

A Reversed  Mode  of  Mixing. — We  have  quite  recently 
experimented  with  pouring  the  bromide  solution  into  the 

* Some  recommend  the  use  of  an  earthenware  hottle,  such  as  an  old  ink- 
bottle.  There  seems  to  be  no  advantage  in  it  if  ordinary  precautions  be 
taken  for  keeping  out  the  light. 


142 


GELATIN O-BROMO-IODI DE  EMULSION. 


silver  solution.  At  first  we  adopted  the  mode  indicated 
above,  of  dissolving  the  bromide  with  the  gelatine.  After 
some  experimental  work,  we  found  that  the  silver  might 
be  mixed  with  the  gelatine,  and  then  the  bromide  added. 
The  method  gives  most  beautifully  fine  emulsions  of  the 
orange  to  ruby  colour,  which  is  such  a desideratum.  The 
method  of  mixing  is  as  follows  : — 

A.  — No.  1 (see  p.  1 39)  is  dissolved  in  1 dr.  of  water. 

B.  — No.  2 is  dissolved  in  1^  ounce  of  water,  and  the 
hydrochloric  acid  dropped  into  it  if  required  (see  p.  139). 

C.  — No  3 is  dissolved  inf  ounce  of  water. 

D.  — No.  4 is  dissolved  in  J ounce  of  water. 

In  the  dark  room , C is  added  to  D,  and  shaken  up 
in  a bottle  till  a perfect  mixture  is  secured,  B is  then 
dropped  in  little  by  little,  and  shaken  up  after  each  addi- 
tion, and  finally  A is  dropped  in.  We  have  never  met  with 
any  red  fog  or  other  disease  induced  by  this  mode  of 
mixing,  and  we  recommend  it  in  preference  to  the  other 
modes  indicated  above. 

A good  Stirring-rod  may  be  made  by  taking  a glass  rod, 
and  tying  across  it  with  clean  string  a strip  of  glass  about 
a couple  of  inches  long  and  half  an  inch  wide.  This 
cross-piece  effectually  stirs  up  the  emulsion  during  its 
formation  by  a motion  of  the  rod  between  the  first  finger 
and  thumb.  We  recommend  its  use. 

Boiling  the  Emulsion. — A saucepan  of  sufficient  size  to 
hold  the  bottle  must  be  procured,  and  filled  with  water 
to  a convenient  height,  and  a flame,  such  as  a gas-burner, 
placed  beneath  it.*  After  the  water  has  been  brought  to 
boiling  point,  the  emulsion  is  kept  boiling  for  twenty 
minutes  to  half-an-hour ; it  being  shaken  at  intervals 
(say  once  every  ten  minutes)  for  half  a minute  or  so.  A 
thick  cloth  tied  round  the  hand  prevents  any  scalding. 
The  boiling,  by-the-bye,  should  take  place  without  the 


* To  prevent  bumping  and  breaking  the  bottle,  we  place  half-a-dozen 
folds  of  blotting-paper  at  the  bottom  of  the  saucepan. 


GELATIN O-BROMO-IODIDE  EMULSION. 


143 


cork  being  left  in  the  bottle,  for  if  it  remain  in,  it  would 
be  blown  out  by  the  force  of  the  steam.  A cork  with  a 
slot  cut  in  it  is,  however,  not  open  to  objection. 

Cooling  and  Washing  the  Emulsion. — After  the  proper 
time  of  boiling,  the  saucepan  is  removed.  The  gelatines 
Nos.  5 and  6 should,  in  the  interval,  be  rapidly  rinsed  in 
several  changes  of  water  to  get  rid  of  any  adherent  dust. 
They  should  then  be  placed  in  a pot  with  2 ounces  of 
cold  water  and  allowed  to  swell.  After  this  they  are 
melted  at  a temperature  of  about  100°,  by  immersing  the 
pot  or  flask  in  hot  water,  and  added  to  the  solution  in  the 
bottle.  Both  the  emulsion , and  also  the  dissolved  gelatine , 
should  be  cooled  to  about  70  to  80°F.by  allowing  water 
from  the  tap  to  run  over  the  jars  before  the  addition  is 
made. 

After  a good  mixing  by  shaking,  the  froth  is  left  to  sub- 
side, and  the  emulsion  is  poured  out  into  a flat  porcelain 
dish,*  and  allowed  to  rest.  The  time  which  it  will  take 
will  vary  according  to  the  temperature  of  the  surrounding 
air,  but  a couple  of  hours  is  generally  amply  sufficient, 
and  often  a much  less  time  will  suffice.!  After  a proper 
consistency  is  obtained  (such  consistency  being  that  the 
gelatine  should  not  tear  with  a moderate  pressure  of  the 
finger),  the  emulsion  is  carefully  scraped  off  the  bottom  of 
the  dish  with  a strip  of  clean  glass,  and  transferred  to  a 
piece  of  very  coarse  canvas  which  has  been  previously 
boiled  in  hot  water  to  get  rid  of  any  grease  or  dirt.  The 
emulsion  is  then  twisted  up  in  this,  and,  by  a gentle 
pressure,  squeezed  through  the  interstices,  the  ball  of 
emulsion  being  absolutely  below  the  surface  of  the  water 


* There  is  no  “ fetish  ” in  a dish.  When  the  emulsion  is  to  be  squeezed, 
if  it  is  set  in  a beaker,  it  turns  out  in  a more  convenient  shape.  In  a dish, 
however,  it  sets  more  rapidly,  since  a greater  surface  is  exposed  to  the  cool 
air. 

t In  very  hot  weather,  if  the  dish  be  stood  in  iced  water,  no  difficulty  in 
setting  will  be  found.  See  subsequent  chapter  for  particulars  of  preparing 
emulsion  at  high  temperatures. 


144 


GELATINO-BROMO-IODIDE  EMULSION. 


into  which  it  is  forced.  The  water  causes  the  threads  of 
gelatine  to  remain  tolerably  separate,  and,  as  it  passes 
through  the  liquid,  most  of  the  soluble  salts  are  at  once 
extracted. 

When  all  is  squeezed  through,  the  particles  of  gelatine 
may  again  be  transferred  to  the  canvas,  and,  after  stretch- 
ing it  loosely  over  the  mouth  of  the  jar  (emptied  of 
water),  may  be  doused  with  water  from  the  tap  or  from  a 
water  jug.  After  a couple  of  gallons  have  been  thus 
passed  over  it,  the  emulsion  should  again  be  squeezed 
through  the  canvas,  and  the  same  operation  repeated, 
thus  exposing  fresh  surfaces  of  gelatine  to  the  action  of 
water.  Alter  another  sluicing  with  water  the  emulsion 
may  be  considered  as  washed,  though,  to  make  assurance 
doubly  sure,  the  gelatine  may  be  left  at  the  bottom  of  the 
jar,  and  the  water  changed  two  or  three  times.  To 
show  the  importance  of  thorough  washing,  the  following 
experiment  may  be  noted.  An  emulsion  was  made  as 
above,  and  after  once  squeezing  through  the  canvas,  a 
part  was  immediately  used  for  making  plates.  A second 
part  of  the  same  w^as  washed  under  the  tap  for  five 
minutes  ; a third  part  was  squeezed  and  washed  a second 
time ; and  a fourth  part  was  allowed  to  soak,  and  squeezed 
a third  time.  The  relative  sensitiveness  of  the  four  parts 
was  as  follows  : — 

1—1 1 — 2i  — 2^ 

The  first  washing  increased  the  sensitiveness  to  one  and 
a-half,  and  the  second  squeezing  to  two  and  a-half,  whilst 
the  third  squeezing  and  washing  had  no  perceptible 
effect. 

The  writer  considers  this  method  of  washing  superior 
to  that  given  below.  Two  squeezes,  it  is  believed,  are 
equal  to  twenty-four  hours’  such  washing.  Gelatine  is 
hard  to  permeate,  and,  being  a colloidal  body,  the  crystal- 
line salt  has  hard  work  to  get  through  when  the  emul- 
sion is  not  finely  broken  up. 


GELATIN O-BROMO-IODIDE  EMULSION. 


145 


Other  Modes  of  Washing  the  Emulsion . — There  are  several 
modes  of  extracting  the  soluble  salts  from  the  emulsion. 
Putting  on  one  side  dialysis  as  introduced  by  Mr.  King, 
owing  to  its  tediousness,  we  pass  on  to  the  most  ordinary 
method.  The  emulsion  when  prepared  is  poured  out  into 
a flat  dish  in  a very  thin  layer  (say)  of  about  £ of  an  inch 
thick.  When  set,  it  is  scraped  off  the  dish  with  a piece 
of  glass,  and  transferred  to  a jar  or  bottle  in  strips.  Mr. 
England  first  scores  it  over  with  the  prongs  of  a silver 
fork,  so  breaking  it  up  into  fine  strips.  Cold  water  is  then 
poured  on  to  it,  and  a stream  of  running  water  kept  flow- 
ing over  it  for  twelve  hours,  more  or  less. 

The  writer  has  converted  a tin  canister  into  an  effective 
washing  apparatus,  as  shown  in  the  figure.  In  the  lid  of 


a common  canister  a hole  is  perforated  so  as  just  to  admit 
of  the  insertion  of  a glass  tube  a,  a ; a piece  of  india- 
rubber  tubing  connects  this  with  the  water  tap,  and  covers 
any  small  chink  between  the  glass  and  the  lid,  as  shown. 
A spout  is  soldered  on  to  the  canister,  as  shown.  A 
bottle  containing  the  emulsion  to  be  washed  is  placed  in 
the  canister,  the  tube  being  inserted  in  it.  The  water 

L 


146 


GELATINOBROMO-IODIDE  EMULSION. 


flows  over  tlie  top  of  the  "bottle,  and  rises  in  the  canister 
to  the  level  of  the  spout,  where  it  trickles  over  into  the 
sink  ; the  heavy  water  containing  the  soluble  nitrate  is 
thus  perpetually  stirred  up  and  caused  to  flow  over  the 
neck  of  the  bottle.  This  answers  admirably,  and  can  be 
used  in  the  daylight,  if  necessary,  but  is  more  applicable 
to  emulsion  that  has  been  cut  into  strips  than  to  that 
which  has  been  squeezed  twice,  as  the  small  particles  are 
apt  to  be  carried  over  the  top  of  the  bottle  and  choke  the 
exit  tube.  A combination  of  this  method  with  that  given 
on  page  143  can,  however,  be  made  by  only  once  squeez- 
ing the  emulsion  through  the  napless  canvas. 

Another  method  is  also  due  to  Messrs.  Wratten  and 
Wainwright,  and  is  as  follows  : — After  the  emulsion  lias 
been  allowed  to  rest  for  two  or  three  hours,  two  ounces 
of  alcohol  to  each  ounce  of  water  used  are  poured  into  the 
bottle  containing  it,  and  well  shaken  up.  The  gelatine 
rapidly  assumes  a pasty  appearance,  and  subsides  to  the 
bottom.  The  bottle  is  then  inverted,  and  the  fluid,  which 
contains  the  soluble  nitrates  and  excess  of  water,  is 
poured  off,  and  may  be  preserved  for  distillation.  The 
explanation  of  the  efficacy  of  this  method  is,  that  the 
alcohol  has  a greater  affinity  for  water  than  has  the  gela- 
tine, and  that  in  extracting  the  water  the  soluble  salts 
are  extracted  with  it.  Methylated  spirit  not  containing 
gum  may  be  used,  and  the  lower  the  specific  gravity  the 
more  effectual  it  is. 

Dr.  Eder,  to  Avhose  careful  researches  photographers  are 
much  indebted,  finds  by  absolute  analysis  that  emulsions 
passed  through  fine  canvas  are  sufficiently  washed  in 
about  thirty-five  minutes  in  running  water,  and  nearly  in 
the  same  time  in  standing  water ; through  coarse  meshed 
canvas  in  one  and  a-quarter  hours  in  running  water,  and  in  a 
much  longer  time  in  standing  water.  When  cut  in  strips, 
it  is  probable  that  twelve  to  twenty-four  hours  may  be 
necessary  to  free  it  sufficiently  from  the  soluble  salts,  in 
order  to  obtain  a maximum  sensitiveness. 


GELATINO-BROMO-IODIDE  EMULSION. 


147 


Draining  the  Emulsion. — When  the  emulsion  is  con- 
sidered to  be  properly  washed,  it  is  then  drained.  This 
the  writer  generally  does  over  the  canvas,  though  some 
recommend  a hair  sieve,  but  it  does  not  appear  that  there 
is  much  advantage  to  be  derived  from  its  use.  The  great 
point  in  either  case  is  to  drain  long  enough.  A couple  ot 
hours  is  sufficient  time,  and  then  the  emulsion  is  ready 
for  melting. 

It  will  sometimes  happen  that  no  amount  of  draining 
over  a hair  sieve  or  canvas  will  render  the  emulsion  suffi- 
ciently free  from  water  to  set  well  when  dissolved  up.  We 
have  found  that  by  pouring  a couple  of  ounces  of  alcohol 
through  the  emulsion  when  draining  that  the  excess  of 
water  is  taken  up,  and  it  becomes  firm.  It  should  be  noted 
that  before  re-dissolving  the  gelatine  it  should  be  firm  and 
free  from  all  sloppiness  (if  such  an  expression  may  be 
used) ; one  dose  of  alcohol  generally  effects  this,  and,  if 
not  one,  two  will.  The  alcohol  may  be  saved  if  required. 
In  case  this  artifice  be  resorted  to,  only  half  the  quantity  of 
alcohol  given  before  should  be  added  to  the  emulsion,  when 
it  is  re-dissolved  for  filtering  and  coating  the  plates. 
Emulsion  that  is  cut  up  into  shreds  is  much  more  easily 
drained  than  that  which  is  squeezed  through  canvas.  It 
is  not  that  the  gelatine  takes  up  more  water,  but  that  the 
water  clings  mechanically  to  the  small  particles  forming  it. 
We  recommend  that  the  canvas  be  as  coarse  as  possible, 
having  a mesh  not  less  than  one-eighth  of  an  inch,  if 
such  can  be  procured. 

Dissolving  the  Emulsion . — After  draining,  the  emulsion 
should  be  transferred  to  a clean  jar  or  jam-pot,  and  then 
placed  in  boiling  water  till  all  the  gelatine  is  thoroughly 
dissolved.  A temperature  of  120°  or  more  more  may  be 
given  it  with  advantage.  The  emulsion,  when  all  addi- 
tions are  made,  will  be  about  6^-  ounces.  The  addition  of 
^ grain  of  chrome  alum  is  to  be  recommended.  This  should 
be  dissolved  in  1 drachm  of  water,  and  added  with  stirring ; 
6 drachms  of  absolute  alcohol  are  next  to  be  added  in  the 


14 8 GELATINO-BROMO-IODIDE  EMULSION. 

same  way,  and  the  emulsion  is  then  ready  for  filtering. 
This  operation  may  he  carried  out  in  various  ways.  The 
writer  now  uses  wet  chamois  leather  or  swansdown  calico, 
which  has  previously  been  well  boiled  and  washed.  This  is 
allowed  to  rest  loosely  in  a funnel,  and  the  emulsion  filters 
slowly  through  it,  all  coarse  particles  being  left  behind.  A 
small  plug  of  washed  wool  is  used  by  many,  and  answers 
well.  It  is  preferable  to  filter  into  a Florence  flask,  as  it 
will  bear  heat,  though  an  ordinary  medicine  bottle  will 
answer  if  the  flask  be  not  at  hand.  The  bottle  or  flask  is 
again  placed  in  water  at  a temperature  of  120°,  and  the 
next  operation  is  to  coat  the  plates. 


CHAPTER  XXYIII. 

BENNETT’S  GELATINO-BROMIDE  PROCESS. 


The  next  process  we  shall  describe  is  that  brought  out 
by  Mr.  C.  Bennett,  and  was  the  first  process  published 
which  gives  extreme  rapidity.  His  description  ot  it  is  ex- 
tracted from  the  British  Journal  of  Photography . Sensi- 
tiveness is  attained  by  slow  digestion  at  a low  temperature 
instead  of  by  boiling.  Mr.  Bennett,  after  describing  the 
light  required  for  the  preparation  of  the  plates,  on  which 
we  have  already  written  (Chapter  IV.),  says  : — 

“ To  make  ‘ assurance  doubly  sure,’  use  a ruby-coloured 
hock  bottle,  and  with  two  eight-ounce  decanter-shaped 
bottles  made  of  test-tube  glass  to  stand  heat,  weigh  out 
for  a ten-ounce  solution — 


Ammonium  bromide 
Best  silver  nitrate 
* Gelatine  ... 
Distilled  water  ... 


...  70  grains 


...  110 
...  200 

...  0 


77 

77 

ounces 


Use  Nelson’s  L No.  1 photographic  gelatine,’  for  with  the 


* It  will  be  noted  that  the  gelatine  and  the  silver  nitrate  have  the  pro- 
portion of  twenty  to  eleven,  or  nearly  two  to  one.  In  the  bromo-iodide 
emulsion  of  the  previous  chapter,  the  proportion  is  four  to  five,  supposing 
the  gelatine  in  which  the  emulsion  is  boiled  is  destroyed.  In  developing  it 
is  evident  the  former  will  require  less  restraining  than  the  latter. 


150  bennett’s  gelatino-bromide  process. 


opaque  sixpenny  packets  you  have  irregularity,  red  fog, 
and  frilling.  Place  aside  four  ounces  of  water  for  the 
bromide,  and  two  ounces  for  the  silver  ; dissolve  the 
bromide  with  heat  in  one  of  the  test  bottles  in  one  or  one 
and  a-half  ounces  of  water  ; pour  into  the  hock  bottle  ; 
swill  out  the  test-tube  with  the  remainder  of  the  four 
ounces  set  aside  for  the  bromide,  and  also  pour  in.  I do 
it  by  heat  to  ensure  all  being  dissolved,  as  it  does  so  very 
slowly  after  the  gelatine  is  inserted.  The  four  ounces  of 
solution  being  now  almost  cold,  add  the  gelatine,  shake 
up  well,  and  place  in  two  or  three  gallons  of  water  at  90°. 
I use  a fish-kettle  with  lid.  [A  good-sized  saucepan  with 
a lid  answered  perfectly  with  the  writer.]  In  two  hours 
the  bromized  gelatine  will,  after  well  shaking,  be  quite 
liquid,  and  also  nearly  at  90°.  Now  dissolve  the 
silver  in  the  other  test  bottle,  to  be  kept  in  one  ounce 
ot  water,  cool  to  90°,  and  pour  in  ; use  the  remainder 
of  the  two  ounces  set  aside  for  the  silver  to  swill 
out,  heat  to  90°,  and  pour  in.  By  being  so  particular 
we  get  regularity,  and  are  able  to  mix  the  plates  of 
different  batches,  which  is  a great  boon.  Shake  the 
emulsion  very  briskly,  and  replace  in  the  kettle  for  two, 
four,  or  seven  days,  according  to  rapidity  required.  The 
temperature  should  never  be  over  90°  ; if  you  do  not  let 
it  exceed  that,  you  will  not  have  red  fog.  1 Cosy  ’ it  up 
with  flannel,  and  it  will  not  lower  many  degrees  during 
the  night.  I,  however,  use  a stove  two  feet  across,  and 
place  it  on  that ; a faint  gas  jet  below  keeps  it  always  at 
90°.  I shake  up  every  twelve  hours.  If  washed  in  two 
days,  the  emulsion  is  rapid  and  dense  ; in  four  days,  more 
rapid  and  less  dense — quick  enough  for  any  drop-shutter 
known,  when  developed  as  below.  With  some  that  I kept 
for  seven  days,  with  drop-shutter,  on  a dull  February 
morning,  pebbles  close  to  the  camera  were  perfectl}7’ 
exposed.  The  negative  was  thin  under  ammonia,  but 
bore  intensifying  to  any  extent. 

u Cool  the  emulsion  in  a bottle  not  smaller  than  a Win- 


bennett’s  gelatino-bromide  process.  151 

Chester  quart,  and  wrap  it  up  in  brown  paper  to  exclude 
all  light  except  the  lip  of  the  neck.  Let  an  india-rubber 
tube  go  quite  to  the  bottom  of  the  bottle  to  stir  away 
those  layers  of  water  which,  on  account  of  greater  specific 
gravity  (by  reason  of  the  salts  they  now  contain),  would 
otherwise  remain  there.  Wash  for  twelve  hours;  a 
dribble  is  sufficient.  Upon  melting  you  have  eight  or  nine 
ounces  of  emulsion ; add  three-quarters  of  an  ounce  of 
pure  alcohol  heated  to  90°  ; fill  up  with  water  (also  warm) 
to  ten  ounces,  and  coat.  The  plates  should  be  only  luke- 
warm, or  you  will  have  red  fog.  For  beginners  it  much 
helps  the  coating  to  double  the  quantity  of  alcohol,  leav- 
ing out  water  to  that  extent.  The  operator  should  not 
be  alarmed  at  the  peculiar  mottling  of  the  film  (due  to 
the  alcohol)  directly  after  coating;  this  subsides  in  a 
few  seconds  to  an  even  surface.  The  extra  alcohol  does 
not  appear  to  alter  the  sensitiveness,  and  is  a great  help ; 
but  with  experienced  workers  it  is  not  necessary,  and  the 
quantity  is  sufficient  to  draw  the  emulsion  up  to  the 
edges,  which  is  the  sole  object  of  introducing  it.  When 
no  alcohol  is  used  you  always  have  thin  edges,  which  is 
very  objectionable,  as  the  negative,  of  course,  will  print 
dark  at  those  parts,  and  this  small  addition  of  alcohol 
totally  rectifies  this  fault.  It  is  difficult  to  measure  the 
exact  quantity  of  emulsion  required  for  each  plate  ; one 
ounce  would  probably  cover  eight  plates  of  6-|  by  4f 
size.” 


CHAPTER  XXIX. 

PAGET  PRIZE  EMULSION. 

The  following  is  the  description  of  the  process  sent  in 
Iby  Mr.  Wilson,  which  won  the  Paget  Prize  Competition 
in  1880 : — 

To  make  a pint  of  emulsion — 

Select  a 20-ounce  narrow-mouth  stoppered  bottle,  with 
a •well-fitting  stopper,  and  thin  bottom.  Make  it  per- 
fectly clean. 

Make  a stock  solution  of — 

Hydrochloric  acid  (pure)  ...  1 fluid  drachm 

Hopkin  and  Williams’  u Pure”  1150  ordinary 
Distilled  water 12 £ ounces 

Put  into  the  20-ounce  bottle — 

20  minims  of  the  above  dilute  acid. 

3 fluid  ounces  distilled  water. 

210  grains  ammonium  bromide. 

(Hopkin  and  Williams’  or  Schering’s,  dry.) 

80  grains  Nelson’s  No.  1 Photo,  gelatine. 

Leave  the  gelatine  to  swell  for  (say)  fifteen  minutes  or 
longer. 

Hie  Addition  of  a Trace  of  Hydrochloric  Acid  to  the  soluble 
bromide  and  gelatine  is  recommended  in  formula  given, 


PAGET  PRIZE  EMULSION. 


153 


for  the  following  reasons : — If  the  soluble  bromide  be 
absolutely  neutral,  and  the  gelatine  a suitable  sample  (see 
page  139),  the  hydrochloric  acid  is  not  necessary , and  better 
omitted.  If,  however,  the  gelatine  be  ever  so  little  alka- 
line, or  even  apparently  neutral,  but  yet  does  not  give  a 
clear  solution,  acid  is  required.  Its  use  is  not  to 
produce  silver  chloride,  but  to  ensure  a fine  precipitate 
of  silver  bromide.  According  to  Mr.  Wilson’s  experience, 
a fine  precipitate  is  hardly  at  all  a question  of  the  method 
of  mixing,  and  elaborate  contrivances  for  the  purpose 
he  considers  as  quite  unnecessary.  A fine  precipitate 
is  easily  obtained,  however  rapidly  the  solutions  be 
mixed,  if  two  conditions  exist,  viz.,  if  the  bromized 
gelatine  solution  contain  a trace  of  hydrochloric  acid, 
and  the  silver  solution  be  not  stronger  than  110  grains 
per  ounce.  If  it  be  50  to  60  grains  per  ounce,  it  may  be 
poured  all  in  at  once ; or  if  a little  weak  solution  be  first 
poured  in,  the  stronger  may  follow  (as  per  formula).  A 
good  test  for  the  suitability  of  a gelatine  is  to  see  if  a 
fine  precipitate  can  be  obtained  without  having  to  add 
hydrochloric  acid.  Too  much  hydrochloric  acid  retards 
or  prevents  the  conversion  of  the  silver  bromide  into  the 
sensitive  form  in  cooking;  a large  excess  destroys  the 
gelatine. 

It  will  thus  be  seen  that  the  addition  of  hydrochloric 
acid  must  be  made  intelligently , according  to  the  other 
materials  accessible. 

It  might  be  supposed  that  any  acid  would  make  the 
precipitate  fine,  and  that,  therefore,  acid  ammonium 
bromide  would  be  good.  Such  is  not  the  case,  and, 
moreover,  the  acid  bromide  has  in  some  way  a powerful 
effect  in  retarding  the  conversion  of  the  silver  bromide 
into  the  sensitive  form. 

Ammonium  Bromide  should  be  as  nearly  as  possible 
neutral.  It  is  usually  more  or  less  acid,  even  though 
otherwise  pure,  and  frequently  becomes  strongly  acid  by 
keeping.  It  is  then  quite  unfit  for  use,  and  will  not  give 
good  results  unless  almost  neutral. 


154 


PAGET  PRIZE  EMULSION. 


Since  sending  in  the  formula  for  competition,  Mr. 
Wilson  has  arrived  at  the  conclusion  that,  on  the  whole,  it 
is  better  to  use  bromide  of  potassium.  The  latter  is 
often  alkaline,  but  may,  without  much  difficulty,  be  ob- 
tained neutral,  and  is  free  from  tendency  to  alter. 

Silver  Nitrate  is  usually — if  good — slightly  acid  with 
excess  of  nitrate  acid.  It  may  be  so  used ; but  it 
was  recently  found  that  better  results  are  obtained 
if  the  silver  solution  be  neutralized  with  carbonate  of 
soda.  A slight  excess  does  no  harm,  as  the  resulting 
trace  of  carbonate  of  silver  is  converted  into  bromide  ; 
indeed,  an  emulsion  may  be  made  by  mixing  washed  car- 
bonate of  silver  with  a soluble  bromide. 

The  uses  of  neutralizing  the  silver  are  twofold.  One 
is,  that  as  the  amount  of  acidity  of  silver  nitrate  varies 
with  different  samples,  it  ensures  the  same  conditions  in 
all  cases ; the  other  is,  that  the  presence  of  nitric  acid  in 
an  emulsion  produces  a tendency  to  green  and  pink  dis- 
colourations  in  the  finished  negative. 

In  another  clean  glass  vessel  (beaker,  measure,  or  flask) 
dissolve  330  grains  nitrate  of  silver  (re- crystallized)  in 
3 ozs.  distilled  water. 

Pour  out  about  2 fluid  drachms  of  this  silver  soluion  into 
another  small  vessel  (say  test  tube),  and  dilute  it  to  half 
strength  with  an  equal  quantity  of  distilled  water. 

Take  the  20-ounce  bottle  and  the  two  lots  of  silver 
solution  into  the  dark  room.  The  writer  prefers  to  use  a 
large  paraffin  lamp,  protected  by  one  thickness  of  ruby 
and  one  of  dark  orange  glass,  to  two  thicknesses  of  dark 
orange  paper  without  any  ruby. 

In  the  dark  room  have  a gas-boiling  stove,  and  on  it  a 
tin  pot  or  saucepan  deep  enough  to  contain  the  bottle 
when  the  lid  is  on.  It  should  have  a tin  perforated  false 
bottom,  to  prevent  the  bottle  resting  immediately  on  the 
true  bottom ; or  a piece  of  wire  gauze  will  answer.  Let 
the  pot  contain  some  three  or  four  inches  in  depth  of 
boiling  water. 


PAGET  PRIZE  EMULSION. 


155 


Turn  out  the  gas  of  the  stove  if  alight,  and  plunge  the 
bottle  into  the  water  two  or  three  times,  so  as  to  avoid 
cracking  it  by  too  sudden  heating ; then  leave  it  in  for  a 
few  minutes,  until  gelatine  is  completely  dissolved.  Do 
not  leave  it  in  longer  than  necessary  for  complete  solution. 
Take  it  out,  shake  up,  remove  the  stopper,  and  set  bottle 
down  on  table  near  your  lamp,  so  that  you  can  see  what 
you  are  doing. 

Pour  in  all  at  once  the  four  drachms  of  dilute  silver 
solution.  Put  in  the  stopper  and  shake  up  thoroughly, 
but  not  too  violently,  for  about  half-a-minute.  Now 
pour  m the  strong  silver  solution  in  quantities  of  about 
half-an-ounce  at  a time,  shaking  as  before  after  each 
addition,  and,  when  all  is  added,  give  a final  thorough 
shaking  for  (say)  a couple  of  minutes. 

If  the  instructions  have  been  so  far  accurately  followed, 
there  will  he  no  coarse  precipitate  or  grit  in  the  finished 
emuliion . 

Now  put  the  bottle  into  the  pot  of  hot  water,  see  that 
the  stopper  is  not  jammed  in,  and  put  on  the  lid.  Light 
the  gas,  and  boil  up  as  quickly  as  possible.  If  the  water 
was  previously  boiling,  and  the  gas  only  turned  out  for 
the  mixing  operation,  it  should  boil  up  in  less  than  five 
minutes  ; then  keep  boiling  for  fifty-five  minutes.  At  the 
end  of  this  time  turn  out  the  gas,  take  off  the  lid,  take 
out  the  bottle,  and  remove  the  stopper  at  once , or  you 
will  not  get  it  out  afterwards.  The  bottle  must  now  be 
cooled  down  as  quickly  as  is  consistent  with  safety  to  the 
glass.  In  very  cold  weather  it  may  stand  on  the  table 
for  ten  minutes  or  so,  and  then  be  cooled  with  water ; 
or,  in  any  weather,  place  it  in  a pan  of  nearly  boiling 
water,  and  cool  gradually  by  allowing  cold  water  to  trickle 
slowly  in,  shaking  the  bottle  occasionally.  Whatever 
method  is  adopted,  it  should  be  down  to  90?  F.,  or  lower, 
in  fifteen  or  twenty  minutes  at  most.  It  cannot  easily  be 
made  too  cold,  as  the  gelatine  has  lost  its  power  of 
setting. 


156 


PAGET  PRIZE  EMULSION. 


In  a glass  beaker  (about  12  or  14-ounce  size)  put 
1 ounce  of  Nelson’s  No.  1 Photo,  or  u X opaque  ” gelatine, 
and  pour  over  it  10  ounces  of  clean  ordinary  water. 
Leave  it  to  soak  until  the  gelatine  has  absorbed  4 ounces 
of  water,  pour  off  the  surplus  6 ounces,  melt  the  swelled 
gelatine  by  immersing  the  beaker  in  hot  water,  and  pour 
it  into  the  20-ounce  bottle  containing  the  cooled  emulsion. 
Shake  up  well,  and  pour  all  back  into  the  beaker,  draining 
out  the  bottle  thoroughly.  Leave  it  to  set  in  a cool  place. 
Mr.  Wilson  prefers  to  leave  it  for  twenty-four  hours.  It 
has  next  to  be  washed. 

The  Addition  of  the  Gelatine  after  boiling  should  be 
made  when  the  boiled  emulsion  and  dissolved  gelatine  are 
both  at  as  low  a temperature  as  possible,  and  between  the 
time  of  this  addition  and  that  of  washing  the  emulsion, 
it  should  be  kept  as  cold  as  possible.  The  reason  of  this 
appears  to  be  that  the  excess  of  alkaline  bromide  has  a 
most  destructive  effect  on  the  new  gelatine,  and  therefore 
the  lower  the  temperature  and  shorter  the  time  during 
which  the  two  are  in  contact  the  better. 

There  is  a curious  effect  depending  on  the  temperature 
at  which  the  emulsion  and  fresh  gelatine  are  mixed,  viz., 
that  if  quite  cold  the  resulting  plate  will  have  a matt  sur- 
face, and  the  higher  the  temperature  the  more  glossy  it 
will  be. 

A plain  solution  of  gelatine  in  pure  water  is  very  little 
injured  by  prolonged  boiling;  but  if  an  alkaline  bromide 
(or  chloride)  be  added,  it  is  speedily  decomposed.  Pro- 
bably the  alkaline  nitrate,  which  is  present  in  the  emulsion 
in  large  quantity,  may  be  even  more  effective. 

For  the  washing,  clean  ordinary  water  at  a temperature 
not  over  50°  F.  should  be  used.  The  writer  prefers  at  all 
times  to  use  water  cooled  down  to  below  40°  by  melting 
ice  in  it.  By  so  doing  uniform  results  are  obtained,  and 
where  ice  can  be  procured  the  cost  is  trifling ; 3 lbs.  of 
ice  will  be  sufficient  for  a pint  of  emulsion  in  the  hottest 
weather. 


PAGET  PRIZE  EMULSION. 


157 


In  a glazed  earthenware  pan  or  other  suitable  vessel, 
put  about  3 pints  of  cold  water,  and  add  3 ounces  of 
saturated  solution  of  bichromate  of  potash  (made  by 
saturating  clean  ordinary  water  with  bichromate,  Hopkin 
and  Williams’  re-crystallized). 

Before  squeezing  the  set  emulsion  through  the  canvas, 
it  should  be  cooled  down  so  as  to  be  as  firm  as  possible. 
If  so,  the  water  into  which  it  is  squeezed  will  remain  al- 
most clear,  or  but  slightly  milky.  If  the  emulsion  be  soft , 
even  though  the  water  be  ice  cold,  the  water  will  be  more 
milky,  and  the  emulsion  take  up  too  much.  Too  much 
excess  of  acid  bromide,  too  high  a temperature  at  the  time 
of  adding  the  gelatine,  or  keeping  at  too  high  a tempera- 
ture between  adding  and  washing,  will  produce  the  same 
result. 

The  emulsion  may,  of  course,  be  washed  by  precipitating 
with  alcohol,  squeezing  the  clot,  breaking  it  up,  and  soak- 
ing in  water  ; but  the  writer  prefers  washing  with  water 
and  bichromate,  as  described,  on  account  of  the  clear  and 
brilliant  shadows  so  obtained. 

Having  cooled  the  beaker  of  set  emulsion  down  to  40° 
F.,  run  a bone  spatula  or  paper  knife  round  and  turn  out 
the  emulsion,  or  cut  it  out  in  lumps.  If  cold,  it  will  come 
out  almost  quite  clean  from  the  glass.  Place  it  on  a piece 
of  coarse 11  straining  cloth”  or  canvas,  and  squeeze  through 
the  meshes  into  the  water,  the  operation  being  performed 
under  the  surface  of  the  water.  Leave  it  so  for  an  hour. 
Lay  the  straining  cloth  over  the  mouth  of  another  pan 
or  large  jar,  and  pour  the  mixture  of  emulsion  threads  and 
liquid  on  to  it  so  as  to  let  the  latter  run  through.  Squeeze 
the  emulsion  a second  time  through  the  cloth  into  clean 
cold  water,  and  immediately  repeat  the  operation  a third 
time,  leaving  the  emulsion  in  the  last  water  for  half  an 
hour.  When  strained  for  the  last  time,  place  cloth  and 
all  in  a large  beaker,  and  put  the  latter  into  hot  water 
until  the  emulsion  is  completely  melted  and  warmed  to 
about  115°  F.,  z.0.,  not  warmer  than  is  pleasant  to  the 


158 


PAGET  PRIZE  EMULSION. 


hand.  With  a clean  hand  take  out  the  cloth  and  squeeze 
it ; very  little  will  he  lost.  The  emulsion  should  now 
measure  about  16  or  17  ounces.  Add  2 ounces  alcohol,  and 
mix  thoroughly.  The  alcohol  may  he  either  pure  ethylic 
alcohol,  sp.  gr.  about  *830,  or  good  colourless  methylated. 
The  writer  prefers  the  former.  If  the  emulsion  now 
measures  less  than  20  ounces,  make  it  up  to  that  by  adding 
clean  water. 

A good  deal  depends  on  the  temperature  at  which  this 
is  done,  and  by  careful  management  much  may  be  effected. 
If  the  emulsion  is  sufficiently  rapid  and  free  from  pink 
and  green  disease,  it  is  best  melted  and  coated  at  a low 
temperature.  If  it  be  slow  and  has  a tendency  to  colour, 
it  will  be  improved  by  heating  to  140°  F.  Mr.  Wilson 
has  had  emulsions  which  became  more  than  three  times  as 
rapid  by  this  treatment ; but  it  is  a somewhat  dangerous 
one,  as  too  high  a temperature,  or  too  prolonged  heating, 
may  result  in  hopeless  grey  fog.  This  kind  of  fog  is  more 
apparent  during  development  than  after  fixing. 

The  emulsion  is  now  ready  for  use.  It  should  be 
filtered  into  the  coating  cup  through  cotton-wool  to  free 
from  bubbles,  and  plates  coated  in  the  usual  way,  dried 
and  used  as  usual  for  rapid  gelatine  plates,  using  about 
an  ounce  of  emulsion  for  a dozen  quarter-plates. 

In  drying  arrangements,  avoid  the  contact  of  gas  or  of 
the  products  of  combustion  of  gas  with  the  moist  plates. 
The  writer  finds  both  to  be  very  injurious. 

Exposure. — As  usual  for  good  rapid  gelatine  plates — 
say  Wratten  and  Wain wright’s  u instantaneous.” 

Development. — Either  pyrogallic,  ammonia  and  bromide, 
or  ferrous  oxalate.  If  the  former,  sufficient  exposure 
and  as  little  ammonia  as  possible  will  give  best  results. 


CHAPTER  XXX. 


BURTON  S PROCESS, 


Mr.  Burton  has  quite  recently  worked  out  a process 
which  certainly  simplifies  the  washing  of  an  emulsion,  hut 
which  at  the  same  time  is  rather  more  expensive,  in  that  it 
requires  the  use  of  spirits  of  wine  or  methylated  spirit  for 
precipitation  purposes.  Mr.  Burton  has  kindly  forwarded 
a statement  of  his  process,  and  we  give  it  as  he  has  de- 
scribed it.  He  prepares  the  following  solutions  : — 

1.  — Silver  nitrate  ...  ...  ...  212  grains 

Water ...  1J  ounces 

2.  — Ammonium  bromide  ...  ...  120  grains 

Ammonium  iodide  ...  ...  10  „ 

Gelatine  (Nelson’s  No.  2 photo- 
graphic)   30  „ 

drobromic  acid  1 drop 


These  are  emulsified  as  given  in  Chapter  XXVII.,  at  page 
140,  or  by  shaking  in  a bottle  as  described  at  page  141. 
There  is  no  reason  why  the  precipitation  should  not  take 
place  by  the  reversed  method  (page  141),  and  we  recom- 
mend it. 

The  emulsion  is  boiled  as  given  at  page  142,  and  is  then 
allowed  to  cool  to  about  50°  or  60^  F.  It  is  then  poured 


ater 


u ounces 


160 


burton’s  process. 


in  a stream  into  6 to  10  ounces  of  alcohol,  the  quantity 
depending  on  the  specific  gravity  of  the  spirit  used ; 
6 ounces  of  absolute  alcohol  suffice,  whilst  it  is  safe  to  use 
10  ounces  with  ordinary  methylated  spirit,  since  it  usually 
contains  a large  quantity  of  water.  The  emulsion  settles 
down  to  the  bottom  of  the  vessel  in  a few  seconds  in  the 
shape  of  a dense  flocculent  precipitate.  Most  of  the 
soluble  salts  are,  of  course,  at  once  extracted,  but  it  is 
better  to  wash  it  further,  either  by  decantation,  or  by 
placing  it  on  a hair-seive  in  running  water ; the  precipitate 
is  coarse  enough  not  to  pass  through  the  meshes. 

In  the  meanwhile  the  following  has  been  prepared  and 
made  into  a solution : — 

Nelson’s  No.  2 gelatine  ...  120  grains 
Autotype  or  Swiss  hard  gelatine  150  „ 

Water ...  12  ounces 

The  bromide  of  silver  precipitate  is  added  to  this,  and 
well  shaken  till  it  is  dissolved  and  all  granularity  has 
disappeared. 

The  difference  between  this  process  and  that  originally 
described  by  Wratten  and  Wainwright  (see  page  146)  is, 
that  in  the  one  case  the  emulsion  containing  all  the  gela- 
tine is  precipitated,  and  in  the  other  but  a small  quantity 
of  gelatine  has  to  be  thrown  down,  and  consequently  the 
elimination  of  the  soluble  salts  in  the  latter  case  is  far 
more  perfect.  There  is  also  a saving  in  alcohol.  To 
prepare  an  emulsion  in  the  shortest  possible  time,  this  pro- 
cess meets  the  requirement,"  since  it  saves  much  time  in 
washing,  and  all  the  time  of  draining. 

Again,  too,  it  will  be  seen  that  this  is  a capital  plan  of 
preparing  dry  pellicle  which  will  keep  indefinitely,  and  the 
bromide  will  remain  in  its  most  sensitive  condition, 
since,  after  precipitation  and  washing,  it  will  rapidly  dry, 
as  the  bulk  of  gelatine  is  so  small,  and  is  in  a granular 
state. 

Mr.  Burton  recommends  the  use  of  acid,  as  it  gives  what 


burton’s  process.  161 

he  happily  calls  a u robust  character”  to  the  emulsion  ; that 
is,  that  the  plate  will  stand  more  rough  usage,  and  more 
forcing  in  development.  The  larger  amount  of  gelatine 
recommended  by  Mr.  Burton  allows  alkaline  development 
almost  unrestrained  by  bromide  to  be  employed,  and  at 
the  same  time  is  no  doubt  economical  in  a pecuniary  point 
of  view ; at  the  same  time,  there  is  no  reason  why  the 
quantity  of  gelatine  recommended  in  Chapter  XXVIL 
should  not  be  used,  in  which  case  the  water  should  be 
reduced  to  7 ounces. 


CHAPTEE  XXXI. 


DR.  EDER’S  PLANS  OF  PREPARING  GELATINE 
EMULSIONS  WITH  AMMONIA. 

One  of  these  methods  is  based  on  the  utility  of  allowing 
ammonia  to  re-act  upon  the  bromide  of  silver  in  its 
original  condition,  which  enables  the  sensitive  emulsion 
to  be  formed  more  rapidly  than  by  Monckhoven’s  method. 
The  second  method,  by  which  greater  sensitiveness  is  ob- 
tained, consists  in  boiling  the  gelatine  emulsion  by  itself, 
and  subsequently  treating  it  with  ammonia  at  95^  F.  for 
half  an  hour.  We  quote  Dr.  Eder’s  own  words  (see 
Photographic  Journal,  November  19,  1880). 

I.  Method  with  Ammonio-Nitrate  of  Silver. — This 
method  furnishes  very  sensitive  plates,  which  are  at  least 
six  or  seven  times  as  sensitive  as  wet  plates.  The 
necessary  operations  are  simple  and  quickly  executed, 
requiring  but  few  apparatus  and  arrangements,  and  may 
be  effected  without  continued  warm  digestion,  a shaking- 
up  arrangement,  a light-tight  cooking-pot,  and  so  on. 
The  requisites  are  an  ordinary  cooking-pot,  a spirit  lamp, 
a thermometer,  and  a reliable  dark-room.  The  plates 
show  great  power  and  density,  and  keep  wonderfully 
clear.  The  emulsion  works  so  clean,  and  is  so  free  from 
granulation,  that  not  only  landscapes  and  portraits  can 
be  taken  with  it,  but  reproductions  of  linear  drawings  can 


GELATINE  EMULSIONS  WITH  AMMONIA. 


163 


Ibe  made  without  intensification.  The  following  is  the 
formula  he  recommends : — 

No.  1. — Potassium  bromide  ...  370  grains 
Gelatine  ...  ...  520  to  700  „ 

Water  10J  ounces 

This  is  dissolved  (as  given  at  page  139)  and  raised  to 
a temperature  of  from  95?  to  120?  F. 

No.  2. — Silver  nitrate  ...  ...  460  grains 

Water  ...  ...  ...  10  J ounces 

Into  this  latter  is  dropped  strong  liquor  ammonia  till 
the  precipitate  is  just  re-dissolved,  and  it  is  then,  in  a ruby 
light,  added  drop  by  drop  to  No.  2,  and  shaken.  The 
flask  containing  the  latter  solution  is  rinsed  out  with 
1J  ounces  of  water,  and  the  emulsion  is  then  placed  in 
a water-bath  at  a temperature  of  95p,  for  from  a quarter 
to  half-an-hour,  gradually  allowing  it  to  cool  down  to  75?, 
but  not  lower. 

The  salts  and  the  gelatine  do  not  require  to  be  so  care- 
fully chosen  for  this  method  as  for  that  which  follows. 
Should  the  bromide  of  potassium  have  an  alkaline  reaction 
it  does  no  harm  in  this  method ; neither  is  the  neutrality 
of  the  nitrate  of  silver  imperative,  nor  the  acidity  of  the 
gelatine ; indeed,  it  may  be  alkaline. 

The  specific  gravity  of  the  ammonia,  regarded  as  a 
determinant  of  its  strength,  is  a secondary  consideration. 
Take  a strong  solution  of  ammonia.  The  proper  quantity 
is  defined  sharply  enough  by  the  sign — u as  much 
ammonia  as  will  re-dissolve  the  precipitate  produced  in 
the  nitrate  of  silver  solution.”  As  one  is  deprived  of 
this  indication  by  which  to  regulate  properly  the  addition 
of  ammonia,  whenever  one  adds  the  ammonia  to  the 
gelatine  containing  bromide  of  potassium  (instead  of  to 
the  nitrate  of  silver),  Dr.  Eder  does  not  so  much  recom- 
mend this  manner  of  mixing,  though,  by  the  alteration 
in  the  procedure,  the  same  sensitiveness  is  obtained  as  by 


164 


GELATINE  EMULSIONS  WITH  AMMONIA. 


the  former  method.*  Great  care  should  he  taken,  when 
adding  the  ammonia  cal  silver  solution,  that  the  tempe- 
rature does  not  rise  too  high,  and  that,  during  the 
digestion,  the  water-bath  does  not  become  too  hot, 
otherwise  fog  is  sure  to  result.  The  temperature  should 
never  exceed  105?  F. 

When  the  digestion  is  finished,  the  emulsion  should  be 
poured  into  a glass  beaker  (one  made  of  not  too  thin 
glass)  or  into  a porcelain  dish,  which  is  placed  in  cold 
water  to  accelerate  the  setting.  When  set  it  is  pressed 
through  canvas  as  used  for  Berlin-wool  work,  and  the  ope- 
ration may  be  conducted  as  given  at  page  143,  and  then 
washed  in  frequently-changed  (or,  better  still,  running) 
water  for  twenty-four  or  forty-eight  hours,  whilst  sus- 
pended in  a coarse  stuff  bag.  A great  deal  of  wafer 
adheres  to  the  gelatine  particle,  which  should  be  allowed 
to  drain  for  at  least  half-an-hour,  either  from  the  bag  or 
else  through  a cloth  filter  placed  loosely  in  a large  funnel. 
If  this  draining  be  omitted,  the  emulsion  will  most  likely 
be  too  fluid.  The  superfluous  water  may  also  be  removed 
with  advantage  by  gentle  pressure. 

The  finely-divided  emulsion  may  either  be  deprived  of 
water  by  placing  it  in  a bath  of  alcohol,  and  then  dried 
in  thin  films  in  the  air,  either  perfectly  or  only  super- 
ficially ,f  or  it  may  immediately  be  liquefied  by  heating  in 
the  water-bath.  Filtration  through  flannel  placed  in  a 
warm  funnel  is  good;  but  it  is  generally  sufficient  to 
allow  it  to  deposit  any  sediment  by  standing  quietly  at  rest. 
If  it  be  intended  to  keep  the  dissolved  gelatine  emulsion 
for  some  time,  an  antiseptic  must  be  added.  To  10  ounces 


* When  gelatine,  bromide  of  potassium,  and  ammonia  are  dissolved,  and 
the  nitrate  of  silver  is  then  added,  the  ammonia  should  not  be  allowed  to 
act  too  long  upon  the  gelatine.  The  ammonia  is  best  added  immediately 
before  the  addition  of  the  nitrate  of  silver  to  the  gelatine. 

t Dr.  Eder  stated  that  he  had  not  tested  this  method  so  minutely  as  to  be 
able  to  maintain  that  it  furnishes  exactly  the  same  product  as  an  emulsion 
immediately  re-dissolved  ; but  that  he  finds  this  preparation  keeps  better 
than  the  dissolved  aqueous  emulsion. 


GELATINE  EMULSIONS  WITH  AMMONIA. 


165 


of  emulsion  add  10  grains  of  salicylic  acid  dissolved  in 
1 drachm  of  alcohol,  or  replace  the  salicylic  acid  by  the 
same  weight  of  thymol  oil,  as  a protection  of  the  gelatine 
against  change  caused  by  long  warming,  putrefaction, 
&c.  The  alcohol  has  a favourable  action,  accelerating 
the  setting  of  the  gelatine  and  the  drying  of  the  film. 

The  proportion  of  bromide  of  potassium  to  nitrate  of 
silver  is  4 : 5 ; it  is  not  advisable  to  take  less  bromide,  as 
one  would  run  the  risk  of  fog.  The  difficulty  of  fixing 
the  proportion  of  the  soluble  bromide  to  the  nitrate  of 
silver  consists  in  finding  the  proper  medium  between  the 
too  much  bromide,  which  retards  the  sensitiveness,  and  the 
too  little,  which  it  is  not  possible  to  overlook,  on  account 
of  the  decomposition  of  the  bromide  of  silver  which  sets 
in,  both  in  the  case  of  treatment  with  ammonia,  and  boiling. 
The  proportions  mentioned  are  those  which  have  been 
found  best  both  by  Captain  Toth  and  Dr.  Eder. 

The  conversion  of  the  insensitive  modification  (which 
transmits  red  light)  into  the  extremely-sensitive  modifi- 
cation (transmitting  blue  light)  takes  place  in  a very  short 
time  when  the  above  directions  are  followed.  Even  at  a 
temperature  of  25°  C.  (77°  F.),  the  complete  conversion 
generally  takes  place  in  from  fifteen  to  twenty  minutes. 
A small  sample  poured  as  a thin  film  on  a sheet  of  glass 
is  sufficient  to  test  whether  the  rays  transmitted,  whether 
of  daylight  or  of  naked  gas  or  candle-light,  are  blue  or 
not.  In  the  former  case  the  digestion  may  be  ended. 
Generally,  the  prolongation  of  the  digestion  over  thirty- 
minutes  develops  no  further  increase  in  sensitiveness 
worth  mentioning;  but  if  the  temperature  be  not  raised 
above  the  point  before  mentioned  there  is,  even  after  three 
hours’  digestion,  no  danger  of  fog. 

If  the  liquid  be  too  hot,  or  the  solution  too  thin  (that  is 
to  say,  too  poor  in  gelatine),  or  if  the  added  ammonio- 
nitrate  of  silver  be  dissolved  in  too  little  water,  the 
bromide  of  silver  will  be  too  coarse  in  the  grain.  It  then 
quickly  settles  at  the  bottom,  and  the  emulsion  becomes 


166 


GELATINE  EMULSIONS  WITH  AMMONIA. 


unequally  mixed.  The  negatives  also  would  be  coarse- 
grained, but  there  would  be,  nevertheless,  no  particular 
increase  observable  in  the  sensitiveness. 

By  the  gentle  heat  prescribed  above,  the  gelatine  should 
not  be  injured  or  changed  that  its  setting  power,  &c., 
should  suffer.  It  is,  therefore,  intentionally  recommended 
to  add  all  the  gelatine  at  once.  By  all  methods  of 
emulsification  with  ammonia  the  separate  addition  of  part 
of  the  gelatine  after  the  digestion  is  ended  is  impractica- 
ble, since  the  greater  pait  of  the  gelatine  must  be  added 
before  the  setting  and  washing,  in  order  to  impart  the 
necessary  solidity  to  the  mass,  and  a renewed  heating  of 
the  emulsion  in  order  to  dissolve  the  additional  gelatine 
would  be  unavoidable.  The  repeated  or  too  prolonged 
heating  of  gelatine  emulsion  containing  ammonia,  as  is 
known,  is  hurtful. 

The  emulsion  must  be  washed  with  great  care.  It  is 
quite  impossible  to  attain  the  full  sensitiveness  ot  the 
plates  in  the  presence  of  any  considerable  quantities  of 
soluble  bromide;  besides  which,  the  slight  residue  of 
ammonia  is  an  enemy  to  the  keeping  qualities  of  dissolved 
emulsion,  because,  even  in  small  quanities,  it  has  a corro- 
sive action,  and  combines  with  the  salicylic  acid,  subse- 
quently added  as  an  antiseptic,  to  the  great  injury  of  its 
property  of  retarding  putrefaction. 

II.  Method  by  Boiling  and  Subsequent  Digestion  with 
Ammonia . — This  is  more  complicated  than  Method  I., 
and  requires  more  care.  It  is  based  on  the  observation 
that  the  modification  of  bromide  of  silver  which  transmits 
blue  light  is  produced  very  rapidly  at  a temperature  of 
from  60°  to  100°  C.  (140°  to  212°  F.),  and  that  the 
sensitiveness  of  such  an  emulsion — already  of  itself  highly 
sensitive — can  be  increased  by  subsequent  treatment 
with  ammonia  at  a gentle  heat,  while  continued  boiling 
would  bring  fog. 

The  proportions  of  the  separate  ingredients  are  the 
same  as  in  Method  I.  (see  page  163).  The  emulsion  is 


GELATINE  EMULSIONS  WITH  AMMONIA. 


167 


then  boiled ; but  during  the  boiling  the  cork  should  not 
usually  be  driven  in  quite  tight,  for  fear  of  the  bottle  being 
shattered  by  the  expansion  of  the  steam.  When  using 
a common  glass  bottle,  change  the  ordinary  cork  for  one 
which  has  a groove  cut  in  it.  The  bottle  filled  with 
emulsion  is  put  in  a perfectly  light-tight  tin  saucepan 
furnished  with  a tight-fitting  lid,*  and  under  the  saucepan 
is  placed  a gas  jet  or  a spirit  lamp,  care  being  taken  that 
not  even  the  reflected  light  from  the  spirit  flame  should 
fall  upon  the  emulsion.  Of  course  it  is  understood  that 
the  whole  operation  takes  place  in  the  dark  room.  The 
boiling  is  continued  for  half  an  hour  from  the  time  the 
emulsion  reaches  100°  F.  (see  page  143). 

The  emulsion  already  possesses  a high  degree  of  sensi- 
tiveness (similar  to  that  of  the  best  commercial  gelatine 
plates),  and  may  be  used  without  any  further  treatment 
with  ammonia.  The  latter,  however,  increases  the  sensi- 
tiveness. When  the  emulsion  has  become  quite  cool  (the 
temperature  may  fall  to  70°  F.),  add  to  it  two  drachms 
of  ammonia,  s.g.  *880,  place  it  in  a water-bath  of  from 
95°  to  100°  F.,  and  digest  at  this  temperature  for  half- 
an-hour  to  an  hour.  At  the  end  of  that  time  the  emul- 
sion is  ready,  and  one  then  proceeds,  after  it  has  set, 
to  wash  it,  &c. 

During  the  subsequent  treatment  with  ammonia  care 
must  be  taken  that  the  temperature  never  exceeds 
105°  F.  Generally,  digestion  for  half-an-hour  suffices, 
but  with  an  hour  one  is  surer  of  having  attained  the 
desired  sensitiveness.  Even  digestion  for  two  hours  does 
not  develop  fog.  The  prolongation  of  the  digestion  with 
ammonia  is  particularly  useful  when  the  previous  boiling 
is  interrupted  before  the  bromide  of  silver  is  sufficiently 
modified.  It  is  assumed,  however,  that  during  the 
whole  process  of  digestion  the  water  never  sinks  below 


* A linen  rag  laid  at  the  bottom  of  the  saucepan  prevents  the  bottle  from 
cracking  in  consequence  of  coming  in  sudden  contact  with  the  hot  metal 
forming  the  bottom  of  the  pot. 


168 


GELATINE  EMULSIONS  WITH  AMMONIA. 


100°  F.  All  the  precautions  described  as  applicable  to 
the  adding  of  ammonia  (Method  I.)  also  apply  here. 

Here  also  all  the  gelatine  must  be  added  at  once ; it 
does  not  do  (as  in  Method  I.)  to  retain  a portion  of  it  and  to 
add  it  later.  Dr.  Eder,  however,  expressly  mentions  that 
with  very  easily-affected  sorts  of  gelatine  one  may  be  in 
a position  to  add  part  of  the  gelatine  when  the  digestion 
is  completely  ended. 

With  regard  to  other  details  (washing,  quantity  of  gela- 
tine, &c.),  the  remarks  made  with  reference  to  the  last 
method  apply  here. 

Dr.  Eder  says  a gelatine  emulsion  prepared  by  Method  II. 
is  more  sensitive  than  one  prepared  by  Method  I.  The 
difference  is,  perhaps,  not  extremely  great,  still  the  sensi- 
tiveness of  that  prepared  by  the  Method  II.  ought  at  least 
to  be  a fifth  greater  than  by  Method  I.  It  gives  negatives 
with  good  gradation,  and  free  from  that  hardness  which 
is  often  seen  in  less  sensitive  emulsions  which  are  difficult 
of  reduction  by  the  developer.  The  whole  picture  gene- 
rally comes  out  pretty  quickly  under  the  developer,  and, 
even  when  the  exposure  is  very  short,  the  shadows  are 
sufficiently  densely  developed  before  the  lighter  parts  have 
become  too  intense.  Dr.  Eder  believes  this  emulsion  will 
be  found  particularly  suitable  for  portraiture  in  the  studio. 
It  can  be  worked  to  opacity,  but  is  less  apt  to  produce 
perfectly  white  or  black  negatives  than  emulsion  prepared 
by  the  first  method. 

To  sum  up  in  a few  words  : — Emulsions  prepared  by 
Method  I.  are  most  suited  for  the  production  of  hard  nega- 
tives, and  those  prepared  by  Method  II.  for  soft  negatives. 
The  former  has  the  same  character  as  the  most  sensitive 
emulsions  at  present  in  the  market ; the  character  of  the 
latter  is  unusual.  Still  it  cannot  be  said  that  with  either , 
both  hard  and  soft  negatives  cannot  be  got  according  to  the 
ivay  they  are  developed. 

In  the  preparation  of  emulsions  by  Method  II.  great  care 
must  be  exercised.  The  gelatine  and  bromide  of  potas- 


GELATINE  EMULSIONS  WITH  AMMONIA. 


169 


sium  should  not  have  an  alkaline  reaction,  for  fear  of  the 
formation  of  fog  during  the  boiling.  The  materials  must, 
therefore,  be  previously  tested  with  litmus  paper/'  If  the 
nitrate  of  silver  be  added  to  the  gelatino-bromide  of 
potassium,  when  heated  to  60°  or  70°  C.  (140°  to  160°F.), 
the  formation  of  the  extremely-sensitive  modification  is 
sooner  produced. 

The  ferrous  oxalate  developer  is  especially  suited  to 
these  fairly  sensitive  gelatine  emulsions,  though  the 
alkaline  developer  may  also  be  used ; the  former  gives 
particularly  clear  and  brilliant  negatives. 


* Should  one  not  be  able  to  obtain  any  neutral  or  slightly  acid  prepara- 
tions, the  hot  solution  of  bromide  of  potassium  and  gelatine  may  be  carefully 
acidified  with  dilute  acetic  acid  or  hydrochloric.  The  reaction  should  be 
only  slightly  acid,  otherwise  the  acetic  acid  will  destroy  the  setting  power  of 
the  gelatine. 


CHAPTER  XXXII. 


A COLD  EMULSIFYING  PROCESS  WITH  AMMONIA. 


Mr.  Henderson  has  experimented  on  wliat  may  be  called 
the  lines  of  Dr.  Eder : viz.,  with  ammonia,  but  using 
the  full  quantity  of  gelatine.  Mr.  A.  Cowan,  however, 
has  made  a modification  which,  we  believe,  has  not  been 
published,  and  this  we  give  as  certainly  the  easiest  form 
of  the  ammonia  process,  and,  so  far,  we  have  proved  it  to 
give  the  best  results  as  regards  rapidity. 

The  same  proportions  of  gelatine,  bromide,  iodide,  and 
silver  are  taken  as  given  at  page  139,  and  dissolved  up  in  the 
same  amount  of  water.  The  silver  should  be  dissolved  in 
cold  water,  and  the  gelatine  solution,  after  dissolving, 
should  be  cooled.  This  can  readily  be  effected  by  making 
the  vessels  containing  the  different  solutions  to  stand  in 
cold  water.  To  the  silver,  however,  is  added  sufficient 
ammonia  (equal  parts  of  ammonia  *880  and  water)  just 
to  dissolve  the  oxide  first  formed.  The  bromide  and 
gelatine  are  then  gradually  added  to  the  ammoniacal  silver 
nitrate,  and  a fine  emulsion  is  formed.  The  remaining 
gelatine  is  dissolved  in  the  same  amount  of  water  as  given 
at  page  143,  and  its  solution  also  should  be  cooled  down. 
This  is  added  to  the  emulsified  bromide,  the  two  are  well 
shaken  up  together,  it  is  then  poured  out  and  set  without 


A COLD  EMULSIFYING  PROCESS. 


171 


further  treatment,  and  washed  in  the  usual  manner.  If  the 
emulsion  he  kept  a day,  it  will  be  found  to  have  great 
sensitiveness. 

The  success  of  this  method  in  giving  sensitiveness 
shows  that  the  sensitive  form  of  bromide  formed  by 
ammonia  is  quickly  arrived  at  in  a but  slightly  viscous 
fluid,  whereas  it  is  not  fully  formed  until  a quarter  to  half- 
an-hour  has  elapsed  (and  even  then  not  unless  the  solution 
be  rendered  less  viscous  by  warming),  when  the  full 
quantity  of  gelatine  is  employed.  There  is  one  thing  that 
has  struck  us  in  using  the  emulsion,  viz.,  the  large  number 
of  plates  that  can  be  coated  with  this  quantity  ot  emulsion 
— nearly  double,  in  fact,  of  those  that  can  be  coated  by  the 
emulsion  formed  as  given  in  Chapter  XXVII.  The 
gelatine,  too,  becomes  softened,  and  it  is  sometimes  advis- 
able to  add  in  a dry  state  40  grains  of  hard  gelatine  to 
the  emulsion  when  washed,  and  before  making  up.  The 
above  quantity  will  coat  forty  7J  by  5 plates. 


CHAPTER  XXXIII. 


A PROCESS  FOR  GELATINE  EMULSION-MAKING 
IN  HOT  WEATHER. 


The  method  adopted  is  very  similar  to  that  described  in 
our  last  chapter,  but  there  are  one  or  two  alterations  in 
procedure.  In  the  first  place,  we  use  the  following  formula, 
which  is  the  same  as  that  given  there,  except  we  substitute 
potassium  for  ammonium  bromide.  It  is  as  follows  : — 


Potassium  bromide 
Nelson’s  No.  1 gelatine 
Water 

Strong  hydrochloric  acid 


250  grains 
45  „ 

1 ounce 

2 drops 


This  is  prepared  in  the  usual  way,  and  warmed  up  to 
120u  F.,  and  the  following  added  as  given  at  Chapter 
XXVII. : — 


Silver  nitrate 
Water 

Finally  to  this  is  added — 
Potassium  iodide 
Water 


...  300  grains 

...  3J  oz. 

...  12  grains 

1 drachm 


The  emulsion  is  then  transferred  to  a glass  flask,  and  boiled 
for  three-quarters  of  an  hour,  shaking  up  the  emulsion  at 
intervals.  This  is  allowed  to  cool  in  the  flask  for  half-an- 
hour,  when  to  it  is  added,  after  dissolving  and  cooling — 
Nelson’s  No.  1 gelatine  ...  ...  120  grains 

Coignet’s,  or  Swiss  hard  gelatine  ...  120  „ 

Water  3 oz. 


GELATINE  MAKING  IN  HOT  WEATHER. 


173 


The  emulsion  is  poured  out  into  a jam-pot,  which  is  imme- 
diately placed  in  iced  water  with  a few  lumps  of  ice  floating 
in  it.  In  half-an-hour  the  gelatine  will  he  firmly  set.  The 
gelatine  is  loosened  from  the  sides  of  the  jam-pot,  and  the 
lump  of  emulsion  is  transferred  into  moist  canvas,  and 
squeezed  through  into  a jar  of  iced  water  (the  water 
having  been  run  through  filter-paper  to  get  rid  of  all 
floating  matter)  in  which  a few  small  lumps  of  washed 
ice  are  floating.  After  ten  minutes  the  water  is  changed, 
and  after  another  ten  minutes  is  changed  again,  when  it 
is  again  collected  in  the  canvas,  and  squeezed  through 
into  water.  One  more  change  of  water  should  he 
sufficient  to  free  it  from  all  except  traces  of  soluble  salts. 
It  is  then  transferred  to  the  canvas,  and  allowed  to  drain 
over  a jar  for  half-an-hour  to  three-quarters  (see  p.  147). 

It  is  again  transferred  to  the  jar-pot  and  melted,  and  two 
or  three  drops  of  carbolic  acid  (or  other  antiseptic)  added, 
and  then  once  more  placed  in  iced  water.  In  half-an-hour 
it  is  set,  when  it  is  covered  with  alcohol  and  allowed  to 
ripen  for  a day  ; and  if  the  jar  be  placed  in  water  con- 
taining a lump  of  ice,  so  much  the  better.  When  plates 
have  to  be  coated,  the  slab  on  which  the  plates  have  to  be 
set  is  covered  with  small  lumps  of  ice  for  half-an-hour, 
and  if  it  be  thick  it  is  only  very  gradually  cooled  ; but,  on 
the  other  hand,  it  also  only  very  gradually  gets  warmed 
again.  During  this  time  the  emulsion  is  melted,  six 
drachms  of  alcohol,  one  grain  of  chrome  alum  in  one 
drachm  of  water  added,  and  filtered.  When  the  plates 
are  coated  (after  the  slab  has  been  dried  from  all  water), 
it  will  be  found  that  the  film  of  emulsion  will  set  in  a 
couple  of  minutes,  and  that  the  slab  remains  cool  enough 
to  enable  five  or  six  batches  of  plates,  each  batch  filling 
the  slab,  to  be  prepared ; that  is,  supposing  your  slab  to 
hold  eight  plates,  you  can  coat  forty  to  forty-eight  without 
re-cooling  the  slab.  The  gas  of  the  drying-box  may  be 
lighted  immediately,  and  the  drying  of  the  plates  will 
proceed  rapidly,  and  not  re-melt.  If  gelatine  be  once  well 


174 


GELATINE  MAKING  IN  HOT  WEATHEK. 


set , it  requires  a high  temperature  to  re-melt  it ; and  the 
more  the  water  is  evaporated,  the  higher  the  temperature 
required.  As  the  current  of  warmed  air  passes  over  the 
plates  the  moisture  is  rapidly  absorbed,  and  hence  the 
drying  can  be  effected  with  safety. 

Supposing  by  any  chance  the  emulsion  appears  too  thin 
before  coating  the  plates,  40  grains  of  Coignet’s  gelatine 
may  be  melted  in  three  drachms  of  water  and  added  to 
the  emulsion,  with  much  stirring,  immediately  before 
filtering. 

It  may  be  said  that  there  is  nothing  novel  in  this  way 
of  proceeding.  It,  however,  contains  a feature  which  has 
not  been  much  practised,  the  value  of  which  was  first 
practically  pointed  out  by  Mr.  W.  B.  Bolton.  He  recom- 
mends hydrobromic  acid  instead  of  hydrochloric.  He 
prepares  a solution  of  this  acid  (s.g.  1*45)  in  distilled 
water  5 parts,  or  hydrochloric  acid  1-20  to  5 parts  of  dis- 
tilled water.  Before  boiling  the  emulsion,  he  adds  a 
couple  of  drops  of  one  of  these  mixtures  to  the  emulsion, 
and  tests  from  time  to  time  for  acidity  by  means  of  test- 
paper.  By  this  means  the  free  ammonia  resulting  from  the 
decomposition  of  the  gelatine  is  neutralized,  and  thus  fog  is 
prevented.  This  plan  of  adding  the  acid  may  be  used 
in  the  method  detailed  in  Chapter  XXVII. ; but  it  is  not 
so  necessary  in  it  as  during  hot  weather,  since  at  the 
temperature  at  which  the  gelatine  sets  in  ordinary  weather 
the  action  of  ammonia  is  not  rapidly  deleterious.  If  the 
gelatine  be  alkaline  in  hot  weather,  even  when  set,  decom- 
position quickly  sets  in.  This  is  the  reason  why  the 
hydrochloric  acid  is  added;  and  since  decomposition  sets 
in  more  easily  in  the  liquid  state  than  in  the  gelatinous 
state,  this  is  the  reason  why  it  is  set  by  means  of  acid. 
The  alcohol  is  used  during  the  ripening  to  prevent  the 
access  of  air  to  it. 


CHAPTER  XXXIV. 

GELATINO-BROMIDE  EMULSION  MADE  WITH 
GLYCERINE. 

The  next  emulsion  is  one  described  in  the  Photographic 
News  by  the  writer.  It  is  a method  of  preparing  an 
emulsion  by  adding  washed  silver  bromide  to  gelatine. 

Let  us  suppose  we  are  going  to  make  up  about  7 ounces 
of  gelatine  emulsion.  W eigh  out  ammonium  bromide, 
140  grains  (or  its  equivalent  in  zinc,  potassium,  or  any 
other  bromide),  and  dissolve  in  20  ounces  of  water  (not 
necessarily  distilled  water).  Next  weigh  out  250  grains 
of  silver  nitrate,  and  dissolve  in  6 ounces  of  water,  and 
add  6 drachms  of  glycerine  to  it,  and  stir  thoroughly  with  a 
glass  rod.  We  prefer  to  put  this  mixture  in  a glass  jar 
holding  about  40  ounces  (an  empty  French  prune  bottle 
would  answer  every  purpose). 

The  bromide  solution  should  now  be  added  very  cau- 
tiously. Take  a 10-ounce  measure,  and  fill  it  up  to  six 
ounces,  or  thereabouts,  so  that  it  is  not  too  full,  and 
gradually  drop,  little  by  little,  the  solution  into  the  silver 
solution,  stirring  very  thoroughly  the  whole  time.  A 
milky  emulsion  forms,  and  gets  thicker  and  thicker 
till  the  whole  bromide  in  the  20  ounces  is  added,  though, 
of  course,  the  fluid  is  per  se  thinner ; a quarter  of  an 
ounce  of  nitric  acid  is  next  added,  and  well  stirred  up. 


176 


EMULSION  MADE  WITH  GLYCERINE. 


This  addition  is  made  to  save  any  chance  of  fog,  which 
might  he  caused  by  the  excess  of  silver  present.  The 
reason  of  this  has  already  been  described  in  Chapter  I. 

This  emulsification  is  better  carried  on  in  a dark  room, 
though  it  is  not  absolutely  necessary.  Ihe  bromide  solu- 
tion must  be  poured  into  the  silver  solution , and  not  vice  versa , 
or  a failure  will  be  most  probable.  The  glass  jar  and  its 
contents  may  now  be  placed  away  into  a cupboard,  and 
left  for  as  long  a time  as  is  convenient,  but  not  for  less 
than  a quarter  of  an  hour.  By  the  latter  time  the  silver 
bromide  will  have  fallen  to  the  bottom  of  the  jar,  with 
the  exception  of  a very  slight  milkiness,  which  will  subside 
in  a couple  of  hours.  The  silver  bromide,  however,  left 
in  suspension  at  the  end  of  the  quarter  of  an  hour  is  so 
small  that  it  may  be  decanted  off  without  detriment  to 
the  emulsion.  The  jar  may  be  tilted,  and  the  liquid 
pouredfoff,  or  a syplion  may  be  introduced  (and  this  is  a 
neater  way),  and  the  liquid  syphoned  off  close  to  the  pre- 
cipitate. About  20  ounces  of  water  are  again  poured 
into  the  jar,  the  precipitate  well  stirred  up,  and  again 
allowed  to  subside.  As  soon  as  ever  the  subsidence  takes 
place,  the  water  is  again  decanted  or  syphoned  off.  This 
operation  is  repeated  four  or  five  times,  after  which  the 
decanted  water  may  be  tested  for  acidity,  and  for  silver 
nitrate. 

To  try  for  the  former,  moistened  litmus  paper  is  held 
over  an  open  ammonia  bottle  till  it  is  thoroughly  blue, 
then  well  washed  in  distilled  water ; this  is  thrown  into  the 
decanted  water.  The  faintest  trace  of  acid  will  redden  it. 
If  it  does  turn  red,  the  washing  must  be  repeated.  To 
test  for  free  silver  nitrate,  add  to  the  wash  water  1 drop 
of  potassium  chromate.  A red  colouration  indicates  the 
presence  of  silver  nitrate.  In  case  of  the  presence  of 
either  one  or  the  other,  as  is  shown  by  the  litmus  paper 
and  the  chromate,  the  washing  must  be  continued. 

The  next  part  of  the  process  has  now  to  be  taken  in 
hand.  100  grains  of  gelatine  are  soaked  in  2 ounces  of 


EMULSION  MADE  WITH  GLYCERINE. 


177 


water;  this  100  grains  should  he  Nelson’s  “No.  1 photo- 
graphic gelatine,”  and  another  100  grains  of  harder  gela- 
tine, such  as  Coignet’s  gold  medal  or  Swiss  hard  gelatine 
in  3 ounces  of  water.  The  vessels  containing  both  these 
(after  the  gelatine  is  properly  swelled)  are  placed  in 
warm  Tvater  of  about  100°  Fahr.,  which  will  gradually 
dissolve  up  the  glutinous  masses.  This  effected,  the 
smaller  lot  is  placed  in  a wide-mouthed  bottle  capable  of 
holding  about  20  ounces  of  fluid,  and  the  washed  silver 
bromide  added  to  it.  The  mouth  of  the  bottle  is  then 
closed  by  a cork  or  bung,  and  the  contents  well  shaken 
up  until  it  becomes  a froth.  It  is  next  placed  in  a kettle 
or  saucepan  containing  warm  water  of  about  100°  Fah., 
and  the  latter  is  held  over  a Bunsen  burner  or  spirit  lamp 
to  keep  up  the  temperature.  When  the  froth  has  sub- 
sided, the  bottle  is  again  shaken,  and  the  warming  process 
repeated.  After  two  or  three  such  shakings  a little  of  the 
gelatine  emulsion  may  be  dropped  upon  a glass  plate, ^.and 
examined  for  granularity,  if  absent,  so  much  the  better ; 
but  if  present,  half  the  second  lot  of  dissolved  gelatine 
must  be  added,  and  the  shaking  repeated. 

If  the  emulsion  be  raised  to  boiling  (as  at  page  142)  for 
five  minutes,  then  shaken,  and  the  same  operation  repeated 
a second  time,  we  believe  that  an  emulsion  is  obtained 
which,  for  rapidity,  will  bear  comparison  with  any  other 
process.  This  plan  will  give  as  smooth  an  emulsion  as 
any  other  method,  provided  the  operator’s  fingers  are  not 
all  thumbs  when  the  bromide  is  dropped  into  the  silver. 

When  the  emulsion  is  ready,  the  remainder  of  the 
gelatine  solution  not  already  added  should  be  poured  into 
the  bottle,  together  with  half  an  ounce  of  alcohol,  and 
after  a final  shake,  and  filtering  through  washed  cotton- 
wool, it  is  ready  for  coating  the  plate.  o 

It  is  more  difficult  to  emulsify  silver  bromo-iodide  in 
this  way,  and  the  more  tedious  method  of  washing  the 
gelatine  emulsion  should  be  resorted  to. 


CHAPTER  XXXY. 


DR.  VAN  MONCKHOVEN’S  PROCESSES. 

1st  Process . — Dr.  Van  Monckhoven,  in  trying  the 
writer’s  original  plan  of  washing  the  silver  bromide  before 
adding  it  to  the  gelatine,  failed,  but  hit  upon  the  following 
ingenious  methods,  which  are  given  in  his  own  words : — 

“I  prepare  very  pure  and  dilute  hydrobromic  acid, 
and  I determine  accurately  the  amount  of  it  required 
to  precipitate  exactly  150  grains  of  silver  nitrate.  I 
then  dissolve  this  quantity  of  acid  in  7 ounces  of  water, 
with  which  I incorporate,  by  heating,  40  grains  of  gela- 
tine. On  the  other  part — and  from  this  moment  I entirely 
operate  in  the  dark  room — I precipitate  150  grains  of 
silver  nitrate  by  a very  slight  excess  of  bicarbonate  of 
soda  ; I let  it  settle  for  twenty-four  hours,  and  then  renew 
the  water  to  the  same  amount,  after  which  I lef  it  settle 
again  previous  to  decanting.  On  this  precipitate  of  silver 
carbonate  I pour  a hot  solution  of  30  grains  of  gelatine  in 
7 ounces  of  water.  This  is  well  stirred,  and  then  I pour 
on  it  the  solution  of  gelatine  and  hydrobromic  acid. 
The  mixture  is  thoroughly  shaken  every  quarter  of 
an  hour,  and  is  kept  at  the  constant  temperature  of 
120°  Fahr.  The  silver  carbonate  dissolves  slowly  in  the 
hydrobromic  acid,  and  the  silver  bromide  is  formed  in  the 
colloidal  liquid  in  a state  of  extreme  sub-division.  At 


monckhoyen’s  processes. 


179 


the  end  of  ten  or  twelve  hours  the  mixture,  when  flowed 
over  glass  plates,  has  a greenish  white  colour.  I next 
introduce  150  grains  of  gelatine,  cut  into  very  thin 
shreds,  which  I dissolve  by  stirring,  and  then,  without 
washing  the  emulsion,  I flow  it  over  the  glass  plate. 

“ In  order  to  obtain  a success  with  this  method  it  is 
necessary  to  take  some  precaution.  The  hydrobromic 
acid  must  be  free  from  phosphorus  and  sulphur ; the 
water  used  for  washing  the  silver  carbonate  must  contain 
no  trace  of  carbonic  acid. 

“In  an  emulsion  prepared  by  this  method  there  is 
always  an  excess  of  hydrobromic  acid  and  of  silver  car- 
bonate, but  I have  satisfied  myself  by  other  experiments 
that  the  presence  of  these  substances  does  not  affect  the 
results.  This  is  not  the  case  if  carbonate  be  replaced  by 
the  oxide  of  silver ; the  emulsion  is  then  grey,  and  gives 
rise  to  fogging.  The  plates  that  I have  prepared  by  this 
method  are  twenty  times  as  rapid  as  the  best  wet  collo- 
dion, and,  compared  with  the  best  English  plates,  I 
have  found  them  to  be  three  or  four  times  as  rapid.  For 
the  rest,  the  same  observations  and  the  same  methods 
apply  also  to  collodio-bromide.” 

2nd  Process . — Dr.  Van  Monckhoven’s  second  process  is 
as  follows : — 

“ Procure  some  of  Nelson’s  No.  1 photographic  gela- 
tine. I insist  upon  this  point,  because  you  will  not 
succeed  with  German  or  French  gelatines,  which  are 
prepared  in  a different  manner  from  those  of  Nelson. 
Weigh  up  exactly  153  grains  of  this  gelatine  and  122 
grains  of  pure  and  well-dried  ammonium  bromide.  Put 
these  two  substances  into  a bottle,  and  pour  upon  them 
10  ounces  of  distilled  water.  In  a quarter  of  an  hour  the 
gelatine  will  have  swollen,  and  you  can  now  put  the 
bottle  into  a warm  water  bath  and  agitate,  in  order  to  dis- 
solve the  two  substances. 

“Weigh  out  184  grains  of  silver  nitrate,  and  dissolve 
in  1J  ounces  of  distilled  water.  Now  pour  the  silver 


180 


monckhoven’s  processes. 


emulsion  into  the  bottle  containing  the  bromide,  a little 
at  a time,  well  shaking  it  after  every  addition.  When 
all  the  silver  solution  has  been  added,  pour  in  1 drachm 
of  pure  ammonia  of  a density  of  *880,  and  shake  up 
well  the  solution.  The  ammonia  exercises  quite  a special 
action  here  ; its  effect  is  to  render  the  emulsion  ready  to 
be  used  in  a few  minutes,  or,  if  great  sensitiveness 
be  required,  it  can  be  obtained  in  a few  hours  instead 
of  days,  and  thus  decomposition  of  the  gelatine  is 
avoided. 

11  Now  pour  the  solution  of  gelatine  into  a porcelain 
dish,  and  place  it  upon  cold  water,  and  let  it  set.  When 
set,  detach  it  from  the  dish,  place  it  in  a strong  linen 
sack,  and  wring  it  so  that  the  gelatine  is  expelled  in 
shreds,  which  are  easily  washed  through  a fine  sieve. 
A washing  of  five  hours  in  water  three  times  changed 
suffices.  Collect  the  pellicle  on  a clean  linen  cloth,  and 
dissolve  it  at  a temperature  of  358  Centigrade,  and  it  is 
fit  for  use.  This  process  is  a combination  of  those  of 
Mr.  Bennett  and  Messrs.  Wratten  and  Wain wright,  with 
this  difference — that  I add  the  ammonia  in  order  to  have 
the  emulsion  ready  to  work  in  a few  hours  instead  of 
days.” 


CHAPTER  XXXVI. 


COLD  EMULSIFICATION  WITHOUT  AMMONIA. 

Mr.  Cotesworth  has  just  described  a plan  of  gaining 
sensitiveness  by  allowing  an  emulsion  to  gain  sensitive- 
ness by  remaining  liquid  at  ordinary  temperatures.  We 
recollect  that  a somewhat  similar  proposal  was  made  of 
emulsifying  at  a low  temperature  in  gum-arabic. 
Following  out  Mr.  Cotesworth’ s general  directions,  we 
have  arrived  at  fairly  satisfactory  results.  An  emulsion  is 
prepared,  as  far  as  the  boiling  operations,  according  to 
Chapter  XXVII.,  the  reversed  mode  of  mixing  (page  141) 
being  preferred.  An  emulsion  which  has  a beautiful  ruby 
colour,  if  kept  liquid,  will,  in  24  hours,  have  attained  a 
grey-blue  colour.  A comparison  with  Bennett’s  process 
(Chapter  XXVIII.)  will  show  that  the  difference  between 
the  two  processes  is,  that  Mr.  Cotesworth  uses  very  little 
gelatine  for  emulsification  to  begin  with,  whilst  Mr.  Bennett 
uses  the  full  quantity.  The  consequence  is  that  the  latter 
gentleman  was  obliged  to  have  recourse  to  prolonged 
emulsification  at  about  95°,  in  order  to  overcome  the 
viscosity  of  the  gelatine,  whilst  the  former  can  get  sensi- 
tiveness in  twenty-four  hours  at  (say)  60°  F. 

In  cold  weather  we  have  found  it  necessary  to  add  a 
couple  of  ounces  of  water  to  the  sensitizing  emulsion,  in 
order  to  prevent  setting.  In  this  case  the  extra  gelatine 
required  is  added  dry,  and,  after  soaking,  the  emulsion  is 
warmed,  and  the  gelatine  melts. 

There  is  nothing  different  in  the  preparation  or  develop- 
ment of  the  plates  to  call  for  any  special  remark. 


CHAPTER  XXXVII. 


PREPARATION  OF  THE  PLATES. 


Cleaning  the  Plates. — Now,  there  is  something  to  say 
as  to  the  mode  of  cleaning  plates,  since  a good  emulsion 
is  often  condemned  for  frilling  when  the  glass  plates  are, 
in  reality,  at  fault.  It  is  our  own  practice  to  immerse 
the  plates  in  nitric  acid  and  water  (1  to  10),  then  to 
wash,  and  next  to  rub  them  once  with  a 10  per  cent, 
solution  of  caustic  potash  or  soda  and  a little  methylated 
spirit.  After  a wash  under  the  tap  the  water  should  flow 
quite  evenly  from  off  them,  when,  after  a rinse  with  distilled 
water,  they  may  be  set  up  to  dry,  which  they  will  do  very 
rapidly  if  allowed  to  stand  on  clean  blotting-paper.  Polish- 
ing  a plate  is  a mistake ; it  only  encourages  the  formation 
of  blisters,  as  it  prevents  the  adhesion  of  the  film  to  the 
glass.  Avoid  French  chalk,  or  anything  but  pure  water, 
and  then  one  of  the  causes  of  frilling  and  blistering  will 
have  been  eradicated.  The  plates  having  been  cleaned  as 
above,  they  are  brought  into  the  dark  room,  which  should, 
if  possible,  be  kept  at  a temperature  between  50°  and  65°, 
as  this  is  the  heat  which  is  most  convenient  at  which  to 
coat  the  plates  and  to  ensure  setting. 

Substrata. — If  it  be  determined  to  use  substrata  to  avoid 


PREPARATION  OF  THE  PLATES. 


183 


frilling  (for  which  it  is  a perfect  cure)  the  following  for- 
mula (Mr.  Forrest’s)  may  be  used  : — 


White  of  egg  ... 
Water 

Methylated  spirit 
Carbolic  acid 


...  1 ounce 

...  20  ounces 
. . . 1 ounce 

...  20  drops 


The  carbolic  acid  is  added  with  stirring  to  the  spirit,  and 
then  the  mixture  poured  into  the  albumen  and  water 
which  has  been  previously  mixed. 

Dr.  Vogel  gives  another  substratum,  which  is  also 
efficacious  and  easily  applied : — 

I. 

Gelatine  50  grains 

Acetic  acid  ...  ...  ...  ounce 


are  placed  in  a bottle  and  warmed  till  solution  takes  place. 
This  keeps  a month. 

II. 

Chrome  alum  ...  ...  10  grains 

Water ...  ...  \ ounce 

is  next  prepared. 


Take  of  No.  I 

No.  II  . 
Methylated  spirit 


. . . 2%  parts 

...  1 part 

...  70  parts 


* and  filter;  coat  the  plates  after  cleaning  and  drying  as 
with  collodion,  and  allow  the  substratum  to  dry. 

We  have  used  a stronger  solution,  and  found  it  also  to 
give  the  required  result : — 


Gelatine  ... 

Acetic  acid 
Alcohol  ... 

Chrome  alum  solution 


...  50  grains 
...  \ ounce 

| ounce 
...  1 drachm 


This  is  applied  like  collodion,  and  gives  a beautifully 


184 


PREPARATION  OF  THE  PLATES. 


bright,  transparent  film.  It  can  be  4 dried  off  ” against 
the  fire,  or  over  a Bnnsen  burner. 

One  ounce  of  water-glass  to  8 ounces  of  albumen  and 
8 ounces  of  water  is  also  to  be  recommended.  Plates  are 
washed,  and  whilst  wet  coated  with  the  above  solution, 
which  is  poured  off  and  allowed  to  dry.  After  drying,  the 
plates  are  again  well  washed  and  dried.  The  substratum 
given  at  page  78  also  answers  perfectly. 

Levelling  Shelf. — The  next  point  to  look  to  is  the  shelf 
on  which  to  lay  the  plates  after  coating.  In  our  own  prac- 
tice we  have  a piece  of  thick  plate  glass  about  3 feet  long 
by  1 foot  broad,  and  f-inch  thick.*  We  level  by  means  of 
three  mahogany  wedges  and  an  ordinary  spirit  level. 


Fig.  13, 


The  level  L is  placed  first  across  the  plate,  and  the  two 
wedges  X and  Y are  altered  till  the  bubble  B of  the  level  is 
central ; the  level  is  then  turned  lengthways  along  the 
plate,  and  the  bubble  caused  to  occupy  its  proper  position  * 
by  shifting  Z,  not  touching  X or  Y.  This  should  cause 
the  plate,  if  true,  to  be  accurately  level ; but  it  is  as  well  to 
repeat  the  operation.  A couple  of  supplementary  wedges 
are  sometimes  useful  if  the  glass  u spring  ” at  all. 

Coating  the  Plate. — The  shelf  being  level,  a plate  is  taken 
on  a pneumatic  holder,  or  held  upon  the  tips  of  the  fingers. 
We  will  suppose  the  plate  is  of  the  by  8^  size  that  is  to 
be  coated.  About  2 ounces  of  emulsion  are  poured  into  a 


* A ground  slate  slab  answers  equally  well. 


PREPARATION  OF  THE  PLATES. 


185 


warmed  measure,  taking  care  that  no  hubbies  are  formed 
(which  can  he  secured  by  pouring  out  the  emulsion  against 
the  side  of  the  measure),  and  a pool  of  gelatine  is  made  at 
the  top  of  the  plate.  It  is  then,  by  careful  pouring,  made 
to  fill  up  the  centre  of  the  plate,  and  flow  to  the  right-hand 
top  corner,  next  to  the  left-hand  top  corner,  then  to  the 
left-hand  bottom  corner,  and,  finally,  to  the  right-hand 
bottom  corner,  where  it  can  be  partially  poured  back  into 
the  measure.  The  amount  used  should  be  noted ; about 
3 drachms  should  be  sufficient  to  well  cover  the  plate. 
The  plate  is  then  detached  from  the  pneumatic  holder 
(if  used),  held  by  the  two  coiners  of  the  diagonal,  and 
quietly  rocked  till  an  even  coating  is  seen  to  be  secured. 
It  is  then  cautiously  slipped  on  the  level  shelf,  and  left  to 
set.  Another  plate  is  taken  and  similarly  treated ; and 
when  the  shelf  is  full,  the  emulsion  on  the  first  plate  will 
have  set,  and  it  must  be  removed  to  the  drying-box  or 
cupboard. 

There  are  other  modes  of  coating  the  plate  to  which  we 
may  refer.  After  a central  pool  is  formed  on  the  plate  as 
above,  the  emulsion  may  be  guided  by  a glass  rod  along 
each  edge,  and  thus  the  chance  of  spilling  is  lessened.  F or 
our  own  part,  we  think  that  this  is  not  a good  plan  ; first, 
because  the  glass  rod  is  liable  to  collect  dust,  as  it  must 
be  wiped  between  coating  each  plate  ; and  secondly,  if  the 
central  pool  of  emulsion  be  not  spread  out  rapidly,  coating 
marks  are  apt  to  be  seen  on  the  finished  negative. 

Another  plan  which  is  advocated  is  to  brush  the  plate 
over  with  a very  thin  film  of  emulsion  by  means  of  a wide 
badger-hair  brush  (kept  in  a small  quantity  of  warm  liquid 
emulsion),  and  then  to  pour  over  the  plate  the  full  quan- 
tity. This  is  not  a bad  plan  if  the  brush  be  kept  clean. 
If  resort  must  be  had  to  any  methods,  our  preference  would 
be  to  use  a ruler  rather  larger  than  the  plate,  one  edge  of 
which  is  covered  with  swansdown  calico,  or  chamois 
leather.  This  should  be  dipped  into  a long  narrow  trough 
of  emulsion  and  swept  along  the  surface  of  the  plate,  and 


186 


PREPARATION  OF  THE  PLATES. 


then  the  emulsion  poured  on  immediately  afterwards.  No 
doubt  with  plates,  to  which  a substratum  is  given  some  such 
artifice  is  almost  necessary. 

Level  Cupboard-shelves. — Instead  of  a levelling  shelf  as 
given  above,  it  is  perfectly  feasible  to  alter  the  cupboard 
shown  at  page  22,  and  the  alteration  does  away  with  the 
drying  markings  sometimes  found,  and  due  to  the  iron 
wires.  The  wires  are  removed,  and  glass  or  slate  strips 
substituted  for  them.  For  plates  8|-by  6£,  slips  3 inches 
wide  are  sufficient,  and  they  should  be  a J-inch  thick  to 
prevent  bending.  One  end  of  the  slip  is  supported  in  a 
stirrup  shown  in  fig.  14,  in  the  top  of  which  is  a slot, 


through  which  a screw  is  passed  into  the  cupboard  ; oppo- 
site to  this  is  another  stirrup  (fig.  1 5),  into  which  are  in- 
serted two  thumbscrews  as  shown.  This  is  placed  exactly 
opposite  the  first  stirrup  in  the  cupboard.  The  strip  is 
placed  between  these  two  stirrups,  and  is  first  levelled 
crossways  by  means  of  the  thumbscrews.  When  level  in 
this  direction  the  length  of  the  strip  is  levelled  by  raising 
or  lowering  the  first  stirrup,  and  when  in  position  the  screw 
in  the  slot  is  screwed  home.  When  once  levelled,  the 
strip  will  always  fall  level  into  position.  In  our  own  cup- 
board we  have  seven  of  such  strips  across  the  cupboard, 
and  they  answer  admirably.  The  coated  plates  are  at 
once  placed  on  these  shelves,  and  allowed  to  set  in  the 
position  in  which  they  are  to  be  dried. 

It  has  been  stated  (though  Ave  have  never  found  it  so) 
that  markings  may  be  met  with  owing  to  the  emulsion 
setting  more  rapidly  in  those  parts  of  the  plate  which  are 
in  contact  with  the  strips.  If  such  should  be  feared,  we 


Fig.  14. 


Fig.  15. 


PREPARATION  OF  THE  PLATES. 


187 


recommend  that  triangular  pieces  of  card  of  inches 
size  should  be  cut,  and  drawing-pins  passed  through 
them  at  each  comer,  and  that  these,  with  points  upper- 
most, should  be  laid  on  the  strips  where  the  plates  have 
to  be  placed.  The  setting  will  then  take  place  without 
any  chance  of  drying  markings,  since  the  plate  will  be 
supported  by  points.  Drawing  pins  may  be  got  by  the 
gross,  all  of  the  same  height.  This  plan  is  very  suitable 
for  warm  weather  when  plates  take  long  to  set.  The 
shelf  in  such  weather  often  becomes  filled  before  the 
plates  are  capable  of  removal  to  the  drying  cupboard. 

Some  dry-plate  makers  prefer  to  dry  their  plates  in  a 
nearly  vertical  position  in  racks,  and  there  is  no  doubt 
that  when  drying  takes  place  in  this  manner  there  is  less 
chance  of  dust  settling  on  the  plates.  At  the  same  time, 
it  must  be  remembered  that  the  plates  must  be  thoroughly 
set  before  they  can  be  placed  in  this  position.  Drying, 
with  coated  face  down,  can  also  be  carried  out  with  a 
little  ingenuity  ; but  we  see  no  special  advantage  in  it. 

Drying  the  Plates. — The  temperature  of  the  cupboard 
should  be  kept  as  even  as  possible,  sudden  changes  being 
detrimental — producing  markings.  Opening  the  drying 
cupboard  door  before  the  plates  are  dry,  when  once  the 
gas  has  been  turned  on,  is  a mistake ; the  plates  should  be 
left  until  it  is  judged  they  are  quite  dry.  Very  quick  dry- 
ing is  a mistake,  as  the  different  layers  of  the  film  get  an 
uneven  strain  which  eventuates  in  frilling.  Six  hours  is 
about  the  minimum  time  which  we  can  recommend,  unless 
drying  by  alcohol  is  resorted  to.  The  temperature  should, . 
if  possible,  not  exceed  80°  F.,  and  the  gas  must  be  regu- 
lated accordingly.  Drying  by  alcohol  is  effected  by 
placing  each  plate,  after  thorough  setting , in  a dish  of  methy- 
lated spirit  free  from  resinous  matter  for  ten  minutes,  when 
it  will  dry  in  an  hour  without  difficulty. 


CHAPTER  XXXVIII. 


DEVELOPMENT  OF  GELATINE  PLATES  WITH 
ALKALINE  DEVELOPERS. 

In  Chapter  II.  we  have  already  shown  the  theory  on  which 
development  proceeds ; hut  here  we  must  enter  a little 
more  fully  into  the  matter.  We  have  shown,  when  the 
alkaline  developer  is  used,  that  as  a rule , a restrainer, 
in  the  shape  of  soluble  bromide,  to  prevent  the  primary 
reduction  of  the  silver  bromide  unaltered  by  light,  is 
requisite.  We  have  italicized  aas  a rule,”  since,  in  some 
cases,  this  restrainer,  which  acts  chemically,  is  really 
unnecessary,  as  a restrainer  which  acts  physically  can 
take  its  place.  This  was  the  case  in  the  old  albumen  beer 
process,  which  was  well  known  till  emulsion  superseded 
it ; the  iodide  in  the  plate  separates  the  particles  of 
bromide  one  from  the  other,  and  the  albumen  wraps  these 
up,  as  it  were,  in  a colloidal  shield,  through  which  the  solu- 
tion finds  its  way  more  slowly  than  it  would  if  they  were 
unshrouded.  Gelatine  is  also  a colloidal  body,  and  we 
may  expect  to  find  the  same  hold  good ; as  a fact,  with 
many  plates  it  does,  and  more  especially  with  those 
plates  which  are  prepared  with  an  emulsion  containing  a 
large  proportion  of  gelatine,!  as  compared  to  the  bromide. 

* If  we  take  emulsion,  for  instance,  prepared  by  Bennett’s  process,  we  find 
that  the  proportion  of  silver  nitrate  to  gelatine  is  11  to  20  ; in  the  formula 
we  have  given  at  page  139  it  is  20  to  16 ; that  is,  in  one  case  the  silver 
nitrate  is  about  $ the  weight  of  gelatine,  and  in  the  other  f ths.  It  can 
thus  be  easily  understood  how  in  one  case  no  potassium  bromide  is  required, 
whilst  in  the  other  a little  is  requisite. 


DEVELOPMENT  WITH  ALKALINE. 


189 


With  some  commercial  plates,  for  instance,  where  the 
silver  bromide  is  minimized,  alkaline  development  may 
proceed  with  the  greatest  ease  without  any  chemical 
restrainer,  the  physical  action  of  the  gelatine  being 
sufficient.  It  is  for  this  reason  that  it  is  difficult  to  give 
any  definite  formula  which  can  apply  to  all  plates.  In 
alkaline  development,  we  may  take  it  that  there  are  three 
components : 1,  pyrogallic  acid ; 2,  ammonia ; 3,  potas- 
sium bromide. 

Before  proceeding  further  we  will  consider  the  different 
functions  of  the  pyrogallic  acid,  the  ammonia,  and  the 
soluble  bromide. 

The  ammonia  and  the  pyrogallic  acid  we  will  take  first. 
As  already  pointed  out  (p.  16),  pyrogallic  combines  with 
the  oxygen,  and  the  bromine  from  the  silver  combines  with 
the  ammonia.  Suppose  we  have  just  sufficient  of  both  to 
complete  the  reaction  indicated,  what  will  be  the  effect  of 
increasing  the  one  or  the  other  ? 

If  the  ammonia  be  increased  we  have  an  increased 
energy  of  the  pyrogallic  acid  for  oxygen,  which  is  to  be 
obtained  from  some  source  or  another.  It  may  obtain  it 
from  the  air,  or  from  the  ammonia  by  developing  the 
image  ; we  may  conclude,  then,  that  the  two  sources  from 
whence  the  oxygen  is  obtained  will  be  used  pretty  equally. 
Hence,  increase  in  ammonia  means  increased  rapidity  of 
development.  It  also  gives  an  increased  amount  of  reduced 
silver  which  may  increase  density,  since  the  pyrogallic  acid 
will  be  used  up  to  the  greatest  extent  possible.  It  will 
also  be  seen  that  the  addition  of  successive  doses  of  am- 
monia to  the  developer  will  give  the  same  result. 

The  addition  of  pyrogallic  acid  to  the  normal  solutions 
means  an  increased  power  of  reduction  and  a larger 
amount  of  oxygen  to  be  absorbed,  and  consequently  more 
silver  to  be  reduced,  but  it  will  be  reduced  more  slowly 
than  where  the  ammonia  is  in  excess.  Now  slow  deve- 
lopment, m a properly  permeable  plate,  means  density, 
since  the  silver  is  reduced  in  a coarser  form,  giving  the 


190 


DEVELOPMENT  WITH  ALKALINE. 


appearance  of  density  with  the  minimum  amount  of 
metallic  silver.  It  must  also  not  he  forgotten  that  pyro- 
gallic  acid  is  per  se  an  absorbent  of  bromine  when  it  has 
no  oxygen  to  absorb. 

In  a 7^  by  5 plate  about  8 grains  of  silver  bromide  are 
reduced  to  the  metallic  state,  and  this  case  from  about 
3-J  grains  of  ammonium  bromide.  A little  calculation  will 
show  that  the  presence  of  2 minims  of  strong  ammonia 
are  necessary  to  cause  this  conversion  in  the  presence  of 
pyrogallic  acid ; and  allowing  for  loss  by  vapourizing,  at 
least  4 minims  should  be  employed.  The  amount  of 
pyrogallic  acid  to  effect  the  same  may  probably  be  placed 
at  about  2 grains,  and  allowing  for  oxidation,  by  contact 
with  the  air,  4 grains  at  least  would  be  necessary  for  the 
full  amount  of  ammonia. 

The  bromide  of  potassium,  or  other  soluble  -bromide, 
slows  the  development,  probably  through  a formation  of 
a double  salt  of  bromide  of  silver  and  potassium,  which 
being  reduced  with  difficulty  retards  reduction,  and  hence 
a greater  apparent  density  of  deposit  is  given  through 
the  slower  development. . 

The  question  then  arises,  should  the  pyrogallic  acid, 
the  bromide,  or  the  ammonia  be  first  applied  to  the  film  ? 
We  believe  that  the  application  of  pyrogallic  acid  first 
has  a slight  tendency  to  slow  the  plate  ; but,  on  the  other 
hand,  it  is  safe  to  do  so,  and  then  subsequently  to  add  the 
other  solutions  together,  little  by  little,  till  proper  density 
is  obtained.  There  can  be  no  doubt  that  flooding  the 
plate  with  the  bromide  solution  first,  is  wrong  in  principle, 
since  bromide  has  a tendency  to  destroy  the  photographic 
image.  On  the  other  hand,  the  first  use  of  an  ammo- 
niacal  solution  has  much  to  recommend  it,  as  pointed  out 
by  Colonel  Wortley  ; it  takes  a minute  quantity  ot  silver 
bromide  into  solution,  which,  on  the  addition  of  pyrogallic 
acid  (and  bromide  if  necessary),  it  is  ready  to  deposit  on 
the  image,  and  at  the  same  time  the  reduction  of  the 
photographic  image  of  sub-bromide  to  the  metallic  state 


DEVELOPMENT  WITH  ALKALINE. 


191 


commences.  The  great  fear  of  this  method,  however,  is  a 
slight  veil.  A safe  plan,  perhaps,  is  to  flood  the  plate  first 
with  ammonia  and  bromide,  and  then  to  add  the  pyrogallic 
acid.  But  on  the  whole,  for  a properly  exposed  plate,  we 
should  recommend  that  all  three  should  be  mixed  in  full 
proportions,  and  applied  at  the  same  time  to  the  film. 
Wetting  the  plate  before  development  is  equivalent  to 
diluting  the  developer,  and,  as  a rule,  is  not  to  be  recom- 
mended except  in  cases  where  there  is  a very  horny  film 
which  requires  softening,  and  then  a slightly  more  con- 
centrated developer  should  be  used. 

Development  of  a gelatine  plate  is  in  reality  an  art  and 
science  combined.  The  art  consists  in  getting  proper 
gradation,  and  the  science  in  mixing  your  solutions  to 
obtain  it.  There  are  only  two  kinds  of  exposed  plates 
which  deserve  attention  at  all : one  when  it  is  exactly 
timed  rightly,  and  the  other  when  it  is  over-exposed.  An 
under-exposed  picture  should  be  washed  off  as  quickly 
as  possible,  or  framed  to  illustrate  u a horrid  example.57 

Before  accepting  what  has  been  laid  down,  the  reader 
is  strongly  recommended  to  make  a few  experiments  him- 
self. First  let  him  take  formulae  such  as  the  following : — 


P. — Pyrogallic  acid  ... 
Water 

B. — Potassium  bromide 
Water  

A. — Ammonia  *880  ... 
Water  


. ...  50  grains 

...  1 ounce 

. ...  50  grains 

1 ounce 

...  2 drachms 

...  2£  ounces 


These  nearly  correspond  to  10  per  cent,  solutions. 
Expose  an  8£  by  6 J plate,  and  cut  it  by  the  diamond  into 
six  parts.  Obtain  a small  dipping  bath  such  as  is  used  for 
quarter-plates,  or  a glass  cell  such  as  is  used  in  physical 
laboratories. 

The  first  experiment,  perhaps,  would  be  to  take 
20  minims  of  P,  and  add  to  it  1 ounce  of  water,  place  it 


192 


DEVELOPMENT  WITH  ALKALINE. 


in  the  dipping  bath,  and  then  immerse  the  end  of  one  of 
the  pieces  of  the  plate  in  it  for  one  to  two  minutes.  Take 
it  out  and  pour  the  pyrogallic  acid  solution  into  the  cup 
in  which  has  been  dropt  40  minims  of  B,  and  80  of  A. 
Develop  the  plate  in  the  dish,  and  note  the  result. 

Other  experiments  of  the  same  type  are,  to  use  the  bro- 
mide first,  then  the  bromide  and  the  ammonia,  and  then 
the  ammonia  alone.  Further  experiments  should  then  be 
made  by  increasing  or  diminishing  the  proportions  of  the 
pyrogallic  acid,  &c.,  when  no  doubt  the  reader  will  be 
able  to  confirm  what  has  been  said  of  the  matter,  or  to 
make  his  own  deductions. 

We  now  come  to  the  development  which  is  most 
suitable  for  any  class  of  plates.  The  method  the  writer 
adopts  is  as  follows.  He  uses  the  solutions  of  the  strength 
given  above,  and  having  exposed  a plate  to  the  sensito- 
meter  (see  Appendix)  he  develops  it  by  taking — 


p 

• • • 

• • • 

...  20  minims 

B 

• • • 

• • • 

...  30  „ 

A 

• • • 

...  60  „ 

Water  ... 

• • • 

• • • 

...  2 ounces 

These  are  mixed  together  and  poured  over  the  plate  lying 
in  a dish,  and  when  fully  developed  the  last  number 
visible  before  fixing  on  the  sensitometer  read.  This 
gives  a correct  idea  of  sensitiveness  of  the  emulsion  used. 
The  number  14  on  Warnerke’s  standard  would  mean  a slow 
plate,  24  a quick  plate.  The  plate  is  then  fixed,  and  the 
density  of  the  first  five  or  six  numbers  ndted.  Suppose — 

1st. — They  are  intensely  opaque. 

2nd. — They  are  about  right  printing  density  for  a 
white  cloud. 

3rd. — They  are  thin. 

To  meet  the  first  case,  the  pyrogallic  acid  should  be  re- 
duced to  10  minims,  and  another  plate  tried.  This  will 
usually  suffice  to  reduce  the  density.  If  not,  a reduction 
of  the  bromide  to  20  minims  may  take  place,  and  this  is 


ALKALINE  DEVELOPMENT. 


193 


sure  to  be  effective,  care  being  taken,  however,  that  this 
last  reduction  does  not  induce  fogging,  in  which  case  the 
ammonia  must  be  diminished. 

To  meet  the  next  case,  the  strength  of  the  pyrogallic 
acid  solution  is  evidently  correct ; a reduction  in  the  bro- 
mide may,  perhaps,  be  made.  A plate  should  be  tried  by 
flooding  it  first  with  the  bromide  and  ammonia  solutions, 
and  then  the  pyrogallic  acid  be  added.  The  plates  should 
then  be  thoroughly  tested  by  a few  further  trials  in 
varying  the  amount  of  ammonia  and  bromide. 

To  meet  the  last  case,  the  pyrogallic  acid  should  be 
increased  to  forty  minims,  and  the  bromide  may  be  also 
increased  to  sixty  minims ; if  this  fails  to  give  density, 
it  is  very  doubtful  if  any  developer  will  gwe  the  required 
intensity,  and  intensification  will  have  to  be  resorted  to 
when  using  this  batch  of  plates.  Be  it  remembered,  how- 
ever, that  a thinly  coated  plate  is  bound  to  give  a thin 
image ; it  is  supposed  that  the  plates  which  are  being  tried 
have  been  properly  coated. 

Having  fixed  the  normal  developer  for  any  particular 
batch  of  plates,  we  have  next  to  consider  how  to  develop 
a negative,  the  exposure  of  the  plate  being  unknown. 
The  above  given  formula  constitutes  a normal  developer 
for  the  emulsion  described  in  Chapter  XXVII.  We 
shall  therefore  use  these  solutions.  The  writer  would 
commence  by  taking — 

A ...  ...  ...  ...  10  minims 

B 5 „ 

Water...  ...  ...  ...  2 ounces 

and  would  allow  the  plate  to  soak  in  this  solution  for  a 
minute.  It  will  be  noticed  that  the  solution  is  weak. 
Into  the  cup  there  should  be  dropped  the  normal  strength 
of  pyrogallic  acid  suitable  for  the  plate  under  develop- 
ment, which  we  will  suppose  to  be  20  minims.  When 
the  A and  B are  returned  to  the  cup,  the  whole  solution  is 
poured  over  the  plate,  and  the  development  watched.  If 


194 


ALKALINE  DEVELOPMENT. 


the  image  begins  to  appear  immediately,  the  developer  is 
flowed  off  and  the  plate  rinsed,  and  into  the  cup  are 
dropped  30  minims  more  of  B and  20  of  A ; the  image  will 
now  appear  more  gradually,  and  increase  in  density ; 
30  minims  more  of  A and  B may  then  be  added,  and  it 
will  be  found  that  the  negative  will  attain  sufficient 
intensity.  There  should  be  no  fogging  of  the  plate  if 
sufficient  bromide  be  used ; this  is  a case  of  over-exposure. 
If  the  image  begins  to  appear  in  about  ten  to  fifteen 
seconds,  it  may  be  presumed  that  the  exposure  has  been 
correct,  and  then  the  full  doses  of  the  ammonia  and  bromide 
A and  B may  be  at  once  added  to  the  cup,  the  developer 
poured  back,  and  used  till  sufficient  intensity  is  obtained. 

Should  the  image  not  appear  for  twenty  seconds,  the 
developer  should  be  poured  away,  the  plate  rinsed,  and  be 
flooded  with  A 60  minims  in  1 ounce  of  water  (supposing 
this  to  be  the  strength  of  ammonia  it  will  bear  in  the 
normal  developer)  ; and  after  a couple  of  minutes  20 
minims  of  B and  20  of  P should  be  dropped  in  the  cup,  and 
development  be  proceeded  with ; if  the  image  appears  in 
two  or  three  seconds,  and  begins  to  get  detail  in  ten,  the 
action  may  be  allowed  to  continue ; if  not,  30  more  of  A 
and  20  of  P should  be  added.  If  this  fails  to  bring  out 
detail,  the  plate  is  hopelessly  under-exposed,  and  no 
amount  of  forcing  will  make  it  yield  a good  negative. 

Such  are  the  outlines  of  development  by  the  alkaline 
method.  It  will  be  seen  that  there  is  more  than  u rule-of- 
thumb  ” work  in  it.  It  requires  an  intelligent  application 
of  the  known  effects  of  the  different  ingredients  composing 
the  developer  to  make  the  best  of  a negative.  There  are 
innumerable  changes  to  be  rung  on  the  three  compounds 
which  make  it  all  the  more  difficult  to  carry  out  properly. 

A general  favourite  with  photographers  is  the  glycerine 
developer  of  Mr.  Edwards,  as  described  by  him,  and  made 
as  follows  : — 

Make  two  stock  solutions,  and  label  them  No.  1 and 
No.  2. 


ALKALINE  DEVELOPMENT. 


195 


No.  1. 

*Pyrogallic  acid  ...  ...  ...  1 ounce 

Glycerine  ...  ...  ...  1 „ 

Methylated  alcohol  ...  ...  6 ounces 

Mix  the  glycerine  and  spirit,  and  add  to  the  pyrogallic 
acid. 

No.  2. 


Bromide  of  potassium  (oi 
nium)  ... 

Liquor  ammonia,  *880 
Glycerine 
Water  ... 


ammo- 


60  grains 
1 ounce 

6 ounces 


The  above  stock  solutions  will  keep  any  length  of  time. 

To  make  the  developer,  add  1 part  of  No.  1 to  15  parts 
ol  water,  and  label  this  bottle  D (developer).  In  another 
bottle  mix  1 ounce  of  No.  2 with  15  ounces  of  water,  and 
label  it  A (accelerator). 

It  will  be  found  convenient,  to  avoid  mistakes,  to  have 
these  two  bottles  of  different  shapes.  Either  of  the  above 
solutions  will  keep  two  or  three  days.  When  required  for 
use,  pour  into  a clean  glass  measure  equal  parts  of  D and 
A,  adding  the  A last  just  before  using.  Place  the  dry, 
exposed  plate  face  up  in  a shallow  dish  or  tray,  and  pour 
the  mixture  steadily  over  the  plate,  avoiding  air-bubbles. 
Should  any  adhere  to  the  surface  of  the  plate,  at  once 
remove  them  with  the  finger,  or  a camel’ s-hair  brush  kept 
for  the  purpose.  Rock  the  dish  gently,  taking  care  to 
keep  the  plate  well  covered  with  the  solution.  In  a few 
seconds  the  image  will  appear,  and,  if  the  exposure  has 
been  well  timed,  ail  the  detail  will  be  out  and  the  deve- 
lopment complete  in  about  one  minute,  when  the  negative 
should  be  well  washed  under  the  tap,  and  placed  at  once 
in  the  fixing  bath. 


* The  writer  believes  that  for  landscape  work  it  is  better  to  reduce  the 
pyrogallic  acid  to  f oz.,  as  too  much  density  is  liable  to  be  given  to  the 
highest  light  with  the  1 oz. 


196 


ALKALINE  DEVELOPMENT. 


Do  not  hurry  the  development,  hut  allow  the  plate  to 
remain  in  the  solution  after  all  the  details  are  visible 
until  the  required  density  is  obtained.  With  this  deve- 
loper, used  in  the  above  proportions,  there  is  no  danger 
of  fog,  except  from  the  action  of  light. 

If,  on  the  application  of  the  mixed  developer,  the  image 
flashes  out  and  the  details  in  the  shadows  appear  too 
quickly,  it  will  indicate  that  the  plate  has  been  over- 
exposed ; therefore  at  once  throw  off  the  mixed  developer, 
and,  without  stopping  to  wash  the  plate,  flood  it  with  D 
alone,  when  the  development  will  be  checked,  and  will 
proceed  more  slowly,  while  the  image  gains  in  density  ; if 
too  slowly,  or  the  negative  appears  to  be  getting  too 
intense,  add  a very  little  of  A.  There  will,  however, 
usually  be  sufficient  of  the  latter  left  on  the  plate  to 
complete  the  development  with  the  simple  addition  of  a 
sufficient  quantity  of  solution  D.  A very  little  experience 
will  enable  the  operator  to  produce  a good  printing 
negative  from  a plate  which,  if  developed  with  the  full 
proportion  of  A,  would  have  been  utterly  useless  from 
over-exposure.  In  very  warm,  bright  weather,  it  will, 
perhaps,  be  found  an  advantage  to  use  rather  more  D than 
A in  the  mixed  developer,  giving  just  sufficient  exposure 
to  avoid  hardness  in  the  negative.  Under-exposure  can 
be  corrected  to  a great  extent  by  increasing  the  propor- 
tions of  A in  the  mixed  developer,  but  the  addition  should 
be  made  at  once  before  the  development  has  proceeded 
too  far,  or  the  effect  will  be  to  increase  the  density,  and 
cause  too  much  contrast  in  the  negative. 

These  concentrated  stock  solutions  will  be  found  very 
convenient  to  use,  and  a great  saving  of  time  in  weighing 
and  measuring  small  quantities. 

The  great  enemies  of  this  developer  are  the  air-bells 
which  form  on  the  plate,  and  they  are  to  be  feared  in  all 
developers  which  contain  glycerine  or  sugar. 

To  develop  plates  made  with  a large  proportion  of  gela- 
tine, we  give  Mr.  Bennett’s  directions  for  development 
with  his  long  emulsifying  process. 


ALKALINE  DEVELOPMENT. 


197 


He  soaks  the  plate  for  a minute  in  water  in  the  deve- 
loping dish,  and  then  pours  the  following  quickly  along 
that  side  of  the  tray  which  is  not  occupied  by  the  plate. 
By  rocking  the  dish  suddenly  it  sweeps  over  the  plate 
(it  is  developed  in  five  to  twenty  seconds)  : — 


Pyrogallic  acid 
Bromide 
Ammonia  (*880) 
Water 


...  1 grain 

. . . none * 

1 to  10  drops f 
...  1 ounce 


He  says  : — Do  not  flood  with  pyrogallic  acid  first,  or  you 
will  render  the  plate  slower ; nor  add  more  pyrogallic,  or 
you  will  again  slow  the  plate,  and,  moreover,  have  it  too 
dense.  It  the  exposure  has  been  sufficiently  short,  you 
should  have  a dense  negative,  with  bare  glass  for  shadows, 
almost  as  soon  as  the  developer  has  covered  it.  If  much 
ammonia  be  used,  and  the  plate  be  not  developed  in  half 
a minute,  fresh  developer  should  be  made,  and  the  plate 
be  washed. 

Mr.  Henderson  recommends  the  use  of  ferro- cyanide 
of  potassium  with  the  ammonia,  and  we  give  a formula. 
Some  find  it  has  a tendency  to  produce  fog,  whilst  others 
have  not  found  this  difficulty  : — 

A nearly  sat.  sol.  of  potassium  ferro- 

cyanide  ...  ...  ...  ...  10  ounces 

Ammonia  ...  ...  ...  ...  10  drops 

Pyrogallic  acid  ...  ...  ...  15  grains 

He  states  that  if  this  developer  be  kept  from  light  and  air, 
it  retains  its  developing  properties  a long  time.  If  it 
refuses  to  develop,  a few  drops  of  ammonia  will  set  its 


* For  reasons  for  this  omission,  see  beginning  of  this  chapter, 
f The  quantity  of  ammonia  depends  on  the  shortness  of  exposure  and 
the  sensitiveness  of  the  plate.  About  4 drops  may  be  considered  as  the 
average  amount  required. 


198 


ALKALINE  DEVELOPMENT. 


developing  power  in  action.  If  free  ammonia  be  present, 
and  it  still  refuses  to  develop,  then  a little  pyrogallic 
acid  must  be  added. 

Nelson’s  developer  is  made  as  follows  : — 


No.  1. 


Pyrogallic  acid  ... 
Methylated  spirit 
White  sugar 
Distilled  water  ... 

1 ounce 
...  7 ounces 

...  1 ounce 

...  3 ounces 

No.  2. 

Ammonia  *880  ... 
Ammonium  bromide 
White  sugar 
Water  ... 

...  4 ounces 

...  1 ounce 

...  J ounce 
...  2 ounces 

Use  40  minims  of  No.  1,  and  from  30  to  40  minims  of 
No.  2,  mixed  in  2 ounces  of  water. 

Messrs  Wratten  and  Wain wright,  with  their  ordinary 
or  slower  plates,  recommend  the  following : — 

I. — Pyrogallic  acid 

Water 

. . . 2 grains 

...  1 ounce 

used  freshly  mixed. 

II. — Potassium  bromide  ... 
Water  ... 

...  15  grains 
...  1 ounce 

III. — Ammonia  (*880) 
Water  ... 

...  1 drachm 

...  1 ounce 

The  plate  is  softened  for  one  minute  in  water,  1 ounce 
of  No.  I.  is  applied  for  one  minute,  and  then  3 minims  of 
II.  and  III.  are  dropped  into  the  developing  cup,  and  the 
pyrogallic  solution  poured  back.  This  is  again  poured  on, 
and  the  image  develops.  When  development  flags,  3 
minims  more  of  No.  II.  and  III.  are  again  added  till 
sufficient  density  is  obtained. 

For  these  rapid  plates  (and,  indeed,  for  most  rapid  plates 


ALKALINE  DEVELOPMENT. 


199 


to  be  found  in  the  market),  and  also  for  plates  prepared 
as  in  Chap.  XXVII.,  use  the  following 


I. — Ammonium  (*880) 
Potassium  bromide 
Water  ... 

II.— Pyro  gallic  acid... 
Water  


...  ...  1 ounce 

...  ...  60  grains 

...  ...  3 ounces 

...  ...  3 grains 

...  ...  2 ounces 


The  plate  is  soaked  in  water  for  a minute,  when  the 
water  is  poured  off,  and  No.  2 substituted.  From  15  to 
20  drops  of  No.  I.  are  poured  into  the  cup,  No.  I.  returned 
into  it,  and  applied  again.  The  plate  develops  rapidly. 
For  our  own  part  we  like  to  add  No.  I.  at  two  intervals  of 
time,  as  the  development  is  more  under  control. 

All  the  above  formulae  are  given  in  the  simplest  possible 
form,  no  additions  being  made.  Many  photographers,  how- 
ever, add  nitric  acid  or  citric  acid  to  the  pyrogallic  acid  to 
keep  it  from  discolouring.  When  using  them,  however, 
it  must  be  remembered  that  a certain  amount  of  ammonia 
is  thereby  neutralized.  If  nitric  acid  be  used,  4 minims 
will  be  sufficient  to  keep  60  grains  of  pyrogallic  acid  free 
from  colour. 

If  citric  acid  about  10  grains  should  be  used,  Mr. 
Berkeley  for  the  same  purpose  uses  about  8 grains  of 
neutral  sodium  sulphite  to  each  ounce  of  water  employed. 
Of  all  additions,  we  may  say  we  prefer  this  last,  since  it 
has  no  neutralizing  effect  on  the  ammonia. 

For  removing  the  yellow  colour  so  often  seen  in  alka- 
line developed  gelatine  negatives,  also  for  the  use  of  the 
alum  bath  to  avoid  frilling,  see  the  chapter  on  u Defects 
in  Gelatine  Negatives.’’ 

The  fixing  bath  used  will  be  found  at  page  209. 


CHAPTER  XXXIX. 


DEVELOPMENT  OF  GELATINE  PLATES  WITH 
FERROUS-OXALATE. 


Development  with  ferrous  oxalate  developer  is  un- 
questionably the  favourite  method  with  the  writer,  though 
his  partiality  for  it  is  not  shared  by  a great  many  photo- 
graphers. F or  purity  of  image  and  general  excellence  of 
quality  he  believes  that  no  developer  can  be  compared 
with  it.  There  can  be  no  doubt  that  it  is  more  expen- 
sive than  the  alkaline  pyrogallate  developer  : but  not  very 
much  so,  since  several  plates  may  be  developed  with  the 
same  quantity  of  developer.  It  must  not,  however,  be 
forgotten  that  after  each  plate  is  developed,  a considerable 
amount  of  soluble  bromide  finds  its  way  into  the  solution, 
owing  to  the  combination  of  the  bromine  liberated  from 
the  reduced  bromide  combining  with  the  potassium  oxa- 
late (see  page  18).  Afler  many  plates  have  been  deve- 
loped, the  solution,  however,  is  not  beyond  use,  since  a few 
drops  of  a weak  solution  of  sodium  hyposulphite  are  most 
effectual  in  giving  it  fresh  developing  power.  We  will 
now  suppose  that  we  have  a plate  to  develop  by  ferrous 
oxalate,  and  trace  the  manipulation  from  the  beginning. 

The  plate  is  taken  out  of  the  slide  in  the  dark-room 
(the  light  dependent,  of  course,  on  the  fact  as  to  whether 


DEVELOPMENT  WITH  FERROUS-OXALATE. 


201 


the  emulsion  has  been  prepared  with  or  without  iodide), 
and  placed  in  a flat  dish  a little  larger  in  bottom  area 
than  itself.  If  the  plate  has  a glossy  surface,  and  has 
been  prepared  with  hard  gelatine,  we  recommend  that  it 
be  soaked  for  five  minutes  in  ordinary  water,  in  order  to 
cause  the  gelatine  to  expand  vertically,  and  so  to  soften  the 
film,  after  which  time  the  water  is  poured  off.  If  the  sur- 
face be  matt,  we  recommend  that  the  plate  be  not  wetted. 
Two  developing  solutions  are  prepared.  A saturated  solu- 
tion of  ferrous  oxalate  in  potassium  oxalate  is  prepared  as 
in  the  Appendix,  and  sufficient  of  it  necessary  to  develop 
all  the  plates  desired  to  do  at  one  time  is  diluted  with  an 
equal  bulk  of  water,' * and  when  the  slight  precipitation  of 
the  yellow  ferrous  oxalate  has  taken  place,  sufficient  of  the 
dilute  solution  to  well  cover  the  plate  is  poured  over  its 
surface,  and  watched  for  half  a minute.  If  the  image 
appears  to  be  developing  fairly  well,  and  detail  coming  out, 
this  developer  is  continued  till  all  detail  appears,  when  it  is 
poured  back  into  a developing  cup,  and  density  obtained 
with  fresh  undiluted  solution  of  ferrous  oxalate,  to  which 
20  drops  to  each  ounce  of  a 20-grain  solution  of  potassium 
bromide  are  added.  This  gives  density.  The  develop- 
ment should  be  continued  till  the  image  appears  well  on  the 
surface  of  the  gelatine  next  the  glass  plate,  supposing  the 
film  to  be  of  medium  thickness.  Many  people  recommend 
the  dish  not  to  be  rocked  to  and  fro  ; but  we  think  it  better 
to  give  a gentle  motion  to  the  liquid,  as  we  have  found  that 
sometimes  fog  is  induced  by  not  doing  so.  The  plate  is 
next  rinsed  under  the  tap,  and  placed  in  the  alum  bath, 
made  as  follows  : — Potash-alum,  a saturated  solution  in 
water.  It  must  not  be  supposed  that  this  bath  merely  pre- 
vents frilling.  It  does  more,  it  decomposes  any  calcium 
oxalate  which  may  be  formed  by  the  water  (containing 


* Perhaps  the  best  plan  is,  when  the  concentrated  solution,  prepared  as 
shown  in  the  Appendix,  is  made,  to  dilute  it  with  on  equal  bulk  of  water 
before  filtering.  Some  ferrous  oxalate  will  be  thrown  down,  and,  of  course, 
can  he  utilized  afterwards. 


202 


DEVELOPMENT  WITH  FERROUS  OXALATE. 


lime)  with  which  the  developer  is  washed  off.  After  a 
couple  of  minutes’  immersion  in  this  bath,  it  is  placed  in 
the  fixing  bath,  and  when  all  the  silver  bromide  and  iodide 
have  been  dissolved,  it  is  washed  under  the  tap,  and  the 
operations  given  at  page  209  repeated. 

Instead  of  the  image  coming  out  properly  with  the 
developer  as  indicated  above,  we  will  suppose  that  after  a 
half  a minute  the  high-lights  only  slightly  appear.  In 
this  case,  to  each  ounce  of  concentrated  developer  20  drops 
of  a solution  of  sodium  hyposulphite  made  as  follows  are 
dropped  into  the  cup,  and  the  dilute  developer  poured  on 
to  the  hyposulphite  : — 

Sodium  hyposulphite  ...  ...  2 grains 

Water  1 ounce 

The  mixture  is  once  more  poured  on  to  the  plate,  and  if 
not  much  under-exposed  for  the  normal  developer,  the 
details  should  ajDpear  rapidly  and  with  good  gradation. 
AVhen  all  detail  is  out  the  plate  is  washed,  and  the  strong 
ferrous  oxalate  solution  with  the  bromide  is  applied  as 
before,  to  secure  density. 

Supposing  the  plate  to  be  over-exposed,  when  the  first 
developing  solution  is  applied,  the  details  will  begin  to 
appear  too  rapidly.  It  should  be  immediately  poured  off, 
and  the  plate  flooded  with  a solution  of  potassium  bro- 
mide (5  grains  to  the  ounce  of  water),  which  should  be 
allowed  to  soak  into  the  film  for  a couple  of  minutes.  It 
is  then  drained  off.  To  each  ounce  of  the  weak  solution 
20  drops  of  the  same  solution  may  be  added,  and  the 
developer  applied  again.  This  should  allow  the  image 
to  come  up  properly  without  flatness,  but  it  may  be 
desirable  to  finish  with  the  strong  solution  as  before. 

It  must  be  recollected  in  using  this  developer  that  the 
addition  of  potassium  bromide  means,  in  reality,  the  con- 
version of  the  bromide  into  bromide  of  iron,  which  is  a 
stronger  retarder  than  potassium  bromide.  Hence  the 
addition  of  the  latter  should  be  made  with  caution. 


DEVELOPMENT  WITH  FERROUS-OXALATE. 


203 


Some  photographers  like  to  use  old  ferrous  oxalate 
solutions,  to  which  sodium  hyposulphite  is  added  at  the 
commencement.  This  no  doubt  gives  brilliant  pictures, 
but  is  apt  to  cause  exposure  to  be  prolonged. 

On  the  whole,  we  recommend  tolerably  fresh  ferrous 
oxalate  if  the  greatest  benefit  is  to  be  obtained  from  the 
developer.  The  developers  made  by  mixed  solutions  of 
ferrous  sulphate  and  potassium  oxalate  (see  Appendix) 
are  not  so  strong  as  those’we  have  supposed  we  are  using  ; 
an  allowance  in  exposure  should  be  made  for  their  weak- 
ness, if  they  are  used.  Either  developer,  however,  can  be 
used  with  the  sodium  hyposulphite,  and  the  difference 
between  their  detail-giving  powers  is  then  very  small. 

There  are  some  plates  which  are  unsuited  for  ferrous 
oxalate  development.  They  are  generally  those  which 
are  prepared  with  soft  gelatine  in  hot  weather.  The  film 
shows  reticulation,  and  the  image  appears  granular.  In 
that  case  resort  should  be  had  to  alkaline  development,  by 
which  this  evil  will  be  lessened.  A plate  worth  using, 
however,  should  always  stand  the  ferrous  oxalate  develop- 
ment. 


CHAPTER  XL. 


INTENSIFYING,  FIXING,  AND  VARNISHING 
GELATINE  NEGATIVES. 

Silver  Intensification . — This  part  of  the  gelatino- 
bromide  process  is  one  which  has  to  be  touched  upon  with 
the  very  greatest  care,  since  all  methods  of  giving 
intensity  have  as  yet  to  stand  the  test  of  time.  Now,  as 
a rule,  a gelatine  negative  has  to  be  intensified  after 
fixing,'*'  since  the  opacity  of  the  film  is  usually  so  great 
that  the  operator  is  unaware  what  density  his  negative 
has  taken  under  development.  The  great  desideratum  is 
a good  silver  intensifier,  but  this  is  fraught  with  so  many 
dangers  that  great  precautions  must  be  taken  to  ensure 
success.  It  may  be  laid  down  as  an  axiom,  that  to  be 
successful  the  whole  of  the  hyposulphite  of  soda  and  silver 
must  be  eliminated  from  the  film,  and  where  the  film  is 
of  any  thickness  this  is  by  no  means  rapidly  effected 
by  simple  washing.  The  writer  finds  after  the  green 
tint  of  the  unacted-upon  salt  has  disappeared  in  fixing, 
the  plate  should  be  placed  in  fresh  hyposulphite,  and 
kept  there  for  a short  time.  This  being  done,  the  plate 
had  better  be  kept  in  water  for  an  hour  or  more,  the 
water  being  changed  at  intervals.  After  this,  the  gelatine 
film  may  be  made  more  secure  by  applying  to  it  a solu- 
tion of  peroxide  of  hydrogen  in  water.  A drachm  of  what 
is  called  a 20-volume  solution  to  5 ounces  of  water  is 


* As  to  intensification  with  silver  befor  e fixing,  see  Appendix. 


INTENSIFYING,  FIXING,  AND  VARNISHING.  205 

sufficient.  When  it  has  soaked  in  this  for  half  an  hour, 
it  is  again  washed,  and  intensification  can  commence. 
Another  plan  is,  after  thorough  washing  to  immerse  the 
plate  in  fresh  alum  solution  for  half  an  hour,  again  wash- 
ing thoroughly,  and  allow  to  dry,  and  then  the  intensi- 
fying may  he  proceeded  with.  Those  who  may  have 
endeavoured  to  intensify  with  pyrogallic  acid  and  silver 
(see  u Appendix  ”)  a negative,  treated  in  the  ordinary 
way  will  find  that  red  stains  occur  almost  invariably 
where  the  film  is  thickest — that  is,  where  the  hyposulphites 
have  not  been  thoroughly  eliminated,  and  to  eliminate 
them  this  extra  precaution  above  indicated  is  necessary. 
The  following  is  recommended : — 

Ferrous  sulphate  ...  ...  5 grains 

Citric  acid  ...  ...  ...  10  „ 

Water  ...  ...  ...  ...  1 ounce 

To  this,  one  or  two  drops  of  a 20-grain  solution  of 
silver  nitrate  are  added,  and  the  plate  intensified  as  if  it 
were  a wet  plate.  Now,  it  by  no  means  follows  that  a film 
thus  intensified  would  be  free  from  a liability  to  change 
in  the  presence  of  light,  since  the  silver  might  partially 
combine  with  the  gelatine.  After  density  has  been 
attained,  the  plate  is  washed  and  put  in  a dish  containing 
common  salt,  and  once  more  passed  into  the  fixing  bath 
fora  few  seconds,  again  washed,  and  then  dried. 

Mr.  Dudley  Radcliffe  has  slightly  modified  the  above, 
and  he,  too,  recognizes  the  importance  of  eliminating  the 
hyposulphites.  To  eliminate  them,  he  places  the  film, 
face  downwards,  in  water  in  a pie-dish,  by  which  the 
heavier  solution  sinks  to  the  bottom.  He  intensifies  with 
the  following : — 

Sulphate  of  iron  and  ammonia  ...  1 ounce 

Lump  sugar  ...  ...  ...  1 „ 

Glacial  acetic  acid  ...  ...  2 ounces 

Albumen  of  ...  ...  u..  1 egg 

Distilled  water ...  20  ounces 


206  INTENSIFYING,  FIXING,  AND  VARNISHING. 


The  albumen  is  added  after  the  other  ingredients  are 
dissolved. 

Success  in  intensifying  by  either  of  these  methods  the 
writer  has  found  to  be  more  certain  when  the  ferrous 
oxalate  developer  has  been  used  in  lieu  of  the  ordinary 
alkaline  developer. 

We  have  heard  of  failures  with  these  methods,  and 
when  traced  to  their  source  have  almost  invariably  found 
that  they  arise  from  intensifying  negatives  which  have 
been  exposed  to  the  air.  It  is  no  uncommon  thing  to  see  on 
such  an  irridescent  film,  to  which,  if  silver  be  applied, 
staining  is  certain.  In  this  case  a very  dilute  solution 
(5  grains  to  the  ounce  of  water)  of  potassium  cyanide 
should  be  applied,  and,  after  well  washing,  the  intensi- 
fication may  begin ; cyanide  will  generally  remove  any 
red  stain  which  may  occur  if  the  above  hyposulphite 
destroying  solutions  have  been  applied  first. 

Mercury  Intensifiers . — The  next  intensifies  are  the 
mercury  intensifiers,  which  may  be  classed  as  most  un- 
uncertain in  their  action  and  in  the  permanency  of  their 
results.  The  negative  can  be  intensified  either  imme- 
diately after  the  washing  which  follows  the  fixing,  or  it 
can  be  employed  upon  a negative  which  has  been  dried. 
In  the  latter  case  the  negative  must  be  steeped  for  a 
minute  or  two  in  water.  Mr.  England  recommends  the 
following  as  giving  him  what  he  desires  : — 

Mercuric  chloride  (bichloride  of 

mercury)  ...  ...  ...  20  grains 

Ammonium  chloride  *..  ...  20  „ 

Water  ...  ...  ...  ...  1 ounce 

After  the  negative  has  been  thoroughly  washed,  the 
above  solution  is  poured  over  it  till  the  surface  assumes  a 
grey  tint.  After  a thorough  wash  (see  page  209)  a weak 
solution  of  ammonia  (10  drops  to  1 ounce  of  water)  is 
applied  till  a dark  tone  is  assumed  by  a reflected  light,  and 
brown  by  transmitted  light.  With  collodion  the  intensity 


INTENSIFYING,  FIXING,  AND  VARNISHING.  207 

thus  given  is  unstable,  and  the  film  has  a tendency  to 
bleach. 

To  Mr.  B.  J.  Edwards,  we  believe,  is  due  the  credit  of 
adding  sodium  hyposulphite  to  the  mercury  intensifier. 
This  formula  is  as  follows  : — 

No.  1. 


Mercuric  chloride  (bichloride  of 


mercury)  ... 

. . . 

...  60  grains 

Water  ... 

No.  2. 

...  6 ounces 

Potassium  iodide 

• • • 

...  90  grains 

Water  ... 

No.  3. 

...  2 ounces 

Sodium  hyposulphite  ... 

...  120  grains 

Water  ... 

• • • 

...  2 ounces 

The  iodide  solution  is  poured  into  the  mercury  solution, 
and  then  the  solution  of  hyposulphite,  which  dissolves  the 
iodide  of  mercury  which  has  been  formed. 

The  negative  is  fixed  and  washed,  and  the  plate  im- 
mersed in  the  above  solution.  Mr.  Edwards  says  of  it : 
u The  intensifier  acts  very  quickly,  a few  seconds  being 
sufficient  to  give  printing  density  to  the  thinnest  negative. 
If  required  to  work  slower,  add  more  hyposulphite,  which 
will  also  alter  and  improve  the  colour  of  the  negative. 
The  shadows  remain  quite  clear,  there  is  no  loss  of 
detail,  and  the  colour  of  the  negative  is  all  that  can  be 
desired.  The  negative  must  finally  be  well  washed.” 
Uranium  Intensifier. — Dr.  Eder,  in  his  u Modem  Dry 
Plates,”  has  recommended  an  uranium  intensifier,  which 
is  made  as  follows  : — 

Uranium  nitrate  ...  ...  15  grains 

Potassium  ferricyanide  ...  15  „ 

Water...  4 ounces 

Before  using  this,  the  plate  must  be  thoroughly  washed 


208  INTENSIFYING,  FIXING,  AND  VARNISHING. 

(see  page  209),  as  traces  of  hyposulphite  cause  a reduction 
of  the  uranic  salt,  and  a consequent  slight  chocolate- 
coloured  veil  over  the  shadows.  The  plate  is  immersed  in 
the  solution,  the  details  in  the  shadows  are  first  attacked, 
and  then  the  half-tones,  and  finally  the  high-lights.  This 
intensification  is  permanent,  and  can  be  used  with  much 
advantage.  Next  to  silver  intensification  we  prefer  this 
one,  on  account  of  its  simplicity  and  permanency. 
Dr.  Eder  says  that  if  a negative  will  not  acquire  sufficient 
intensity  with  uranium,  it  may  be  laid  aside  as  useless, 
and  with  this  we  agree. 

Varnished  negatives  may  be  intensified  by  removing 
the  varnish  first  in  warm  methylated  spirit,  and,  after 
rinsing  under  the  tap,  a tuft  of  cotton-wool  should  be 
applied  to  the  surface.  We  think  that  there  is  but  little 
more  to  be  said  regarding  intensifying  a negative.  If  it 
be  weak  and  full  of  detail,  we  much  prefer  to  make  a thin 
transparency  by  contact,  and  from  this  another  negative 
also  by  contact.  By  this  means  proper  intensity  can  be 
given  to  the  reproduced  negative,  which  it  is  almost  im- 
possible to  give  to  the  original,  so  that  all  the  rapidity 
of  the  gelatine  plates  is  secured,  together  with  the  ad- 
vantage of  the  collodion  film  for  intensifying.  We  can. 
strongly  recommend  this  plan  to  our  readers,  as  it  has  been 
most  successful  in  our  hands. 

Another  plan  of  getting  intensity,  which  is  said  to  be 
successful,  "was  one  recommended  by  Mr.  Kennett,  which 
is  as  follows  : — 

To  3 ounces  of  water  add  1 ounce  of  sodium  hyposul- 
phite, to  another  3 ounces  add  1 ounce  of  ferrous  sulphate 
(proto-sulphate  of  iron),  mix,  and  allow  them  to  stand 
a short  time.  When  the  plate  has  been  well  washed  after 
development,  it  is  placed  in  this  mixture,  and  the  image 
will  be  fixed  and  intensified  to  an  intense  black.  A great 
advantage  of  this  fixing  solution  is  that  the  ferrous  sul- 
phate acts  on  the  gelatine  as  a hardening  solution,  being 
even  more  astringent  than  alum. 


INTENSIFYING,  FIXING,  AND  VARNISHING.  209 


Fixing  the  Negatives . — The  formula  for  the  hyposulphite 
fixing  solution  has  been  given  at  page  101,  and  need  not 
be  repeated.  The  strength  there  noted  is  perhaps  rather 
great  for  many  commercial  plates,  and  it  might  be  made 
up  to  about  1 ounce  of  hyposulphite  to  a half-pint  of  water* 
This  reduces  the  chance  of  frilling.  The  use  of 
cyanide  is  inadmissable,  as  it  attacks  the  image  (see 
page  211). 

Before  fixing  the  negative,  it  may  be  advisable  to  avoid 
all  danger  of  frilling,  and  immerse  it  in  an  alum  bath, 
which  consists  of  a saturated  solution  of  crystallized 
potash  alum.  The  negative  should  be  rinsed  both  before 
and  after  immersion.  Five  minutes  in  such  a bath  should 
be  sufficient.  The  plate  is  next  rinsed  and  placed  in  the 
fixing  bath,  and  here  it  is  that  the  use  of  iodide  in  the 
emulsion  is  disadvantageous.  The  hyposulphite  attacks 
iodide  much  less  rapidly  than  it  does  bromide ; hence  a 
plate  prepared  with  iodide  takes  longer  to  fix. 

After  fixing  the  negative,  it  has  to  be  thoroughly  washed 
(unless  it  has  to  be  intensified  by  Edwards’  intensifier,  see 
page  207).  There  are  various  contrivances  for  effecting 
this.  A trough  with  vertical  grooves  to  fit  the  plate  is 
sometimes  employed,  which  is  a good  plan  where  many 
negatives  have  to  be  washed,  since  the  heavier  saline 
solution  sinks  to  the  bottom  of  the  water  with  which  the 
trough  is  filled.  Where  only  a few  negatives  are  to  be 
washed,  flat  dishes  answer,  about  four  changes  of  water 
being  given,  each  change  being  made  at  the  end  of  every 
half  hour.  To  ensure  thorough  elimination  of  the  hyposul- 
phite, the  plate  may  be  subsequently  immersed  in  the 
alum  bath,  and  again  washed.  It  must  be  recollected 
that  thorough  washing  of  any  film  depends  on  its  thick- 
ness, and  we  may  say  that,  as  a rule,  we  consider  six  hours 
not  too  long  washing  for  a thick  film.  When  the  plate 
is  considered  washed,  if  it  is  not  to  be  intensified,  it  may 
be  placed  in  a rack  and  allowed  to  dry  spontaneously. 
If  rapid  drying  be  required,  it  may  be  flooded  three 


210  INTENSIFYING,  FIXING,  AND  VARNISHING. 


times  with  methylated  spirit,  when  it  will  dry  very 
readily,  and  can  even  be  accelerated  by  a gentle  heat. 

Varnishing  the  Negative. — In  order  to  prevent  staining 
of  the  film  by  contact  with  silver  paper  during  printing, 
coating  of  varnish  should  be  applied  to  the  negative  ; 
but  in  order  to  avoid  any  chance  of  marking  of  the  film, 
and  before  any  varnish  is  applied,  it  is  preferable  that  it 
should  receive  a coating  of  plain  collodion.  If  it  has 
received  one  to  avoid  frilling,  it  will  be  unnecessary  to  give 
it  another.  When  the  collodion  is  used,  the  writer’s  expe- 
rience tells  him  that  almost  any  varnish  will  answer. 
Enamel  collodion  is,  perhaps,  the  best  to  employ ; or  it 
may  be  made  by  dissolving  6 grains  of  tough  pyroxyline 
in  half-ounce  of  ether  and  half-ounce  of  alcohol  (*820). 
The  collodion  is  poured  in  a pool  at  the  upper  end  of 
the  dried  plate,  and  flowed  first  to  the  right-hand  top 
corner,  next  to  the  left-hand  top  corner,  third  to  the  left- 
hand  bottom  comer,  and  finally,  as  much  as  possible  is 
drained  off  in  the  bottle  at  the  bottom  right-hand  corner, 
giving  the  plate  a gentle  rocking  motion  in  order  to  cause 
all  lines  to  coalesce.  The  plate  is  then  set  up  and  allowed 
to  dry.  For  a varnish,  Mr.  England  uses  seed  lac  in 
methylated  spirit  (a  saturated  solution),  and  then  thinned 
down  till  it  is  of  a proper  consistency.  The  Autotype 
Company  prepare  a special  varnish  for  gelatine  plates,  as 
does  Mr.  Hubbard  one  to  use  as  a retouching  medium. 
To  apply  the  varnish,  the  plate  should  be  gently  warmed 
over  a spirit-lamp  or  before  the  fire  to  such  a heat  that 
the  back  of  the  hand  can  only  just  bear  the  touch  of  the 
plate.  The  varnish  is  applied  like  the  collodion.  After 
draining  of  all  excess,  and  rocking  the  plate,  it  is  warmed 
till  all  spirit  has  evaporated  and  till  the  film  is  glossy.  A 
lack  of  warmth  will  cause  the  film  to  dry  u dead.” 
Where  many  prints  are  not  to  be  taken,  it  is  believed 
that  the  film  of  collodion  alone  is  a sufficient  protec- 
tion against  the  silver  nitrate  of  the  paper  combining 
with  the  gelatine,  and  so  causing  a discolouration. 


INTENSIFYING,  FIXING,  AND  VARNISHING.  211 


If  a negative  does  get  discoloured  through  this,  a very 
dilute  solution  of  potassium  cyanide  will  usually  clear 
away  any  marking  that  may  have  been  made.  But  great 
care  must  be  taken  in  using  this  solvent  of  the  silver 
compound,  as  it  attacks  metallic  silver  when  in  such 
a state  of  fine  division  as  that  in  which  it  is  to  be  found 
in  the  gelatine  plate. 


CHAPTEK  XLI. 


GELATINO-CHLORIDE  EMULSION. 


Dr.  Eder  and  Captain  Pizzighelli  have  recently  worked 
out  a most  satisfactory  gelatino-chloride  emulsion,  and, 
more  important  still,  a satisfactory  method  of  developing 
it  when  it  is  made.  We  have  already  alluded  to  it  in 
Chapter  XX.  The  formula  they  give  is  as  follows  : — 

Sodium  chloride  ...  ...  grains 

Gelatine,  hard  and  soft  (mixed)  25  „ 

Water  ...  ...  ...  ...  3J  dr. 

This  is  emulsified  by  adding  to  it  15  grains  of  silver  dis- 
solved in  2 drachms  of  water.  The  silver  may  be  precipi- 
tated and  re-dissolved  by  ammonia,  as  given  in  Chap- 
ter XXXI.,  or  it  may  be  boiled  and  treated  with 
ammonia,  as  given  in  the  same  chapter. 

F or  our  own  part  we  prefer  to  use  the  boiling  method, 
and  to  use  the  equivalent  of  sodium  chloride  for  the 
ammonium  bromide,  omitting  the  iodide,  as  given  in 
the  standard  formula  in  Chapter  XXVII. 


GELATINO-CHLORIDE  EMULSION. 


213 


The  formula  thus  stands  : — 


(2)  Sodium  chloride 

(3)  Nelson’s  No.  1 Gelatine 

(4)  Silver  nitrate  ... 

(5)  Nelson’s  No.  1 Gelatine 

(6)  Coignet’s  gold  medal  gela-) 

tine,  or  Swiss  gelatine  } 


80  grains 


30 

200 

80 

80 


?? 

5J 

J? 

JJ 


To  emulsify,  we  prefer  the  u reversed  mode  of  mixing,” 
using  the  quantities  of  water,  &c.,  described  on  pages  141 
and  142.  The  emulsion  is  boiled  for  half  an  hour,  which 
changes  the  original  canary-colour  to  blue-grey,  a similar 
change  to  that  effected  in  a bromide  emulsion. 

Development  is  effected  by  the  ferrous-citro-oxalate 
developer,  and  also  by  hydrokinone  (see  page  238). 

Dr.  Eder’s  developer  is  given  at  page  237,  and  can 
be  used  with  advantage,  though  it  requires  a rather  pro- 
longed exposure. 

Contrary  to  the  opinion  of  Dr.  .Eder,  who  places  the 
maximum  effect  of  the  spectrum  on  silver  chloride  in 
the  indigo  about  the  line  G,  we  have  made  it  invariably 
at  H,  or  near  the  visual  limit  of  the  violet  end  of  the 
spectrum.  It  is  for  this  reason  that  this  emulsion 
is  very  much  more  rapid  in  the  spring  and  summer 
and  early  autumn  than  in  the  winter  and  late  autumn. 
We  believe  that  on  a bright  summer’s  day  (when  the  ultra- 
violet rays  are  abundant)  it  is  as  rapid  as  a good  many 
bromide  emulsions.  If  an  emulsion  containing  silver 
iodide  be  made  by  omitting  10  grains  of  sodium  chloride, 
and  substituting  for  it  3^  grains  of  potassium  iodide,  an 
emulsion  is  made  which  can  be  developed  with  ferrous 
oxalate  without  any  restrainer  whatever,  though,  except 
for  shortening  the  time  of  development,  it  has  no  advan- 
tage over  the  ferrous-citro-oxalate. 

The  development  is  carried  out  in  a dish  as  usual. 

Plates  prepared  with  this  emulsion  should  be  carefully 
kept  from  the  air,  since  they  are  apt  to  get  tarnished,  and 


214 


GEL ATINO-  CHLORIDE  EMULSION. 


then  develop  badly.  If  they  are  wrapped  in  paper  as 
described  in  the  Appendix  they  may  be  kept  an  unlimited 
time. 

We  give  an  interesting  table  formed  by  Dr.  Eder  of  the 
sensitiveness  of  silver  chloride  emulsion  as  compared  with 
silver  bromide  in  gelatine. 


Sensitive  Substances. 

Neoessary 
time  of  ex- 
posure to 
bring 
about  a 
vigorous 
image. 

Sensitive- 
ness of  the 
combina- 
tions. 

AgBr  developed  with  ferrous  oxalate  or  alkaline  pyro- 
gallic  

1 

100 

AgBr,  with  aoid  pyrogallic  aeid,  ferrous  sulphate,  and 
silver  nitrate  

5-7 

16-20 

Agl  ditto  ditto 

4-5 

20-25 

AgCl  with  alkaline  pyrogallic 

6-8 

13-17 

AgCl  with  ferro-citrate  and  a trace  of  hyposulphite  ... 

10 

10 

AgCl  with  ferro-eitrate  alone 

60 

2 

AgCl  with  pyrogallic  acid  alone  

100 

1 

AgCl  with  hydrokinone  and  ammonium-carbonate  ... 

160 

0’7 

AgCl  with  hematoxylin  and  ammonium-carbonate  ... 

600 

0-2 

AgCl  without  development,  commenceemnt  of 
blackening 

150-200 

•05--07 

CHAPTER  XLII. 


GELATINIZED  PAPERS. 

There  are  in  the  market  at  the  present  time  two  or  three 
gelatinized  papers  containing  silver  bromide,  and  it  is  to 
be  presumed  that  these  papers  are  prepared  with  gelatine 
emulsion.  At  first  sight,  nothing  would  appear  simpler 
than  to  coat  paper  with  an  emulsion,  but  we  may  at  once 
say  that  it  is  not  by  any  means  so  simple  as  it  seems.  We 
will  endeavour  to  give  a description,  however,  of  a plan 
by  which  it  can  be  accomplished  in  a satisfactory  manner. 
Firstly,  the  emulsion  may  be  gelatino-bromide,  gelatino- 
bromo-iodide,  or  gelatino-chloride,  and  may  be  prepared 
by  any  of  the  methods  given  in  the  previous  chapters. 
It  may  be  boiled  or  not  boiled,  according  as  great  or  little 
sensitiveness  is  required.  For  our  own  part,  we  like  a 
paper  which  is  only  moderately  sensitive,  since  there  is 
no  great  need  to  take  extremely  rapid  pictures.  One 
thing,  however,  we  may  remark,  that  with  bromo-iodide 
and  bromide  emulsions  the  colour  resulting  from  a boiled 
emulsion  has  a tendency  to  be  less  green  than  one  pre- 
pared without  boiling.  This  remark  also  applies  to 
gelatino-chloride  emulsion,  but  with  not  such  force. 

The  amount  of  water  with  which  the  finished  emulsion 
is  made  will  be  found  to  be  about  correct ; but  the  operator 
must,  by  an  experiment  with  an  emulsion,  judge  whether 


216 


GELATINIZED  PAPERS. 


the  gelatine  he  uses  should  he  increased  or  diminished. 
A hard  gelatine,  for  instance,  may  allow  dilution  with 
water.  A golden  principle  to  remember  is,  however,  that 
the  thicker  you  require  your  film,  the  less  water  there 
should  be  with  the  gelatine.  If  a film  is  wanted  as  thick 
as  that  for  carbon  printing,  it  can  be  obtained  by  using 
100  grains  of  gelatine  to  each  ounce  of  water,  instead  of 
about  <a:s  much  to  4 ounces  of  water.  If  a thick  film,  how- 
ever, be  required,  we  recommend  that  the  operations  we  are 
going  to  describe  be  repeated  twice — or  even  three  times. 

The  paper  to  be  coated  may  be  medium  Saxe  paper,  or 
paper  of  that  description,  with  not  too  high  a glaze  on  it. 
It  should  be  cut  up  into  the  sized  sheets  required,  and  care- 
fully dusted  from  every  particle  of  dust.  The  emulsion 
should  be  heated,  and  placed  in  a shallow  dish  somewhat 
larger  than  the  sheet  to  be  coated,  and  the  fluid  should  be  a 
quarter  of  an  inch  in  depth.  The  dish  must  be  kept  warm 
by  placing  it  on  a closed  shallow  tin  box  containing  water 
heated  by  a spirit  lamp  beneath,  or  some  other  similar 
means.  When  heated  to  about  1302  F.  (the  temperature 
depending  upon  the  kind  of  gelatine  employed),  the  paper 
is  turned  up  for  about  a quarter  of  an  inch  at  one  end,  and 
the  sheet  coiled  up  in  a roll,  the  coil  being  made  towards 
the  turned-up  end.  The  turned-up  end  is  placed  on  the 
emulsion,  and  the  coil  gradually  allowed  to  unrol  itself 
till  the  whole  surface  except  the  turned-up  end  rests  upon 
the  emulsion.  After  resting  a minute  the  end  is  seized  by 
two  hands,  and  a glass  plate  having  been  made  to  rest  on 
the  dish,  the  uncoated  side  of  the  paper  is  drawn  on  to  the 
plate,  where  it  remains  till  it  is  set,*  when  it  is  hung  up  by 
clips  to  dry  in  a cupboard  or  other  place  free  from  dust. 
The  paper  thus  prepared  should  present  an  even  film,  free 
from  all  u ridges”  or  “tear-markings,”  and,  when  deve- 
loped, should  present  a vigorous  image  by  transmitted 


* It  is  a good  precaution  to  take  to  place  a muslin-covered  frame  over  the 
glass  holding  the  gelatinized  paper  to  protect  it  from  dust. 


GELATINIZED  PAPERS. 


217 


light.  To  develop  a bromide  or  bromo-iodide  emulsion  we 
recommend  a ferrous  oxalate  developer,  using  to  every 
ounce  employed  about  10  drops  of  a 20-grain  solution  of 
potassium  bromide.  This  gives  a blacker  image  than  the 
ferrous  oxalate  alone.  The  Photographic  Artists’  Co- 
operative Supply  Association,  who  issue  paper  as  above, 
recommend  the  following  form  of  ferrous-oxalate  : — 


Stock  Solutions. 

1.  — Chrome  alum  ... 

Boiling  water  ... 

2.  — Oxalic  acid 

Water  ... 

A.  — Potassium  oxalate 

Glycerine 

Chrome-alum  solution  (No.  1) 
Oxalic-acid  solution  (No.  2).. 
Water 

B.  — Ferrous  sulphate 

Sulphuric  acid 
Water  ... 


100  grains 
5 ounces 
30  grains 
5 ounces 
4 ounces 
J ounce 
jl 

2 5? 

* „ 

15  ounces 

4 ounces 
10  minims 

16  ounces 


To  develop,  8 parts  of  A are  mixed  with  1 part  of  B. 

An  excellent  developer  may  be  made  by  mixing  equal 
portions  of  the  ordinary  oxalate  developer  (see  Appendix) 
and  the  above.  For  fixing — 


Sodium  hyposulphite  4 ounces 

Water  ...  ...  ...  ...  20 


if 


They  further  recommend  the  following  for  bleaching 
necessary : — 

A saturated  solution  of  borax  or 

sulphuric  acid ...  ...  ...  1 ounce 

Water  ...  ...  ...  ...  100  ounces 


And  to  harden  the  film,  common  alum  (a  saturated  solu- 
tion), or  chrome  alum  of  a strength  20  grains  to  each 
ounce  of  water. 


218 


GELATINIZED  PAPERS. 


F or  a charming  black  tone  we  recommend  that  boiled 
chloride  emulsion  be  used.  It  is  very  easily  prepared,  and 
presents  great  facility  of  development  with  the  ferrous- 
citro-oxalate  developer  given  in  the  Appendix.  The 
bromide  and  bromo-iodide  papers  may  also  be  developed 
with  the  usual  alkaline  developer,  using  citric  acid  to  keep 
the  solutions  from  discolouring.  The  addition  of  sodium 
sulphite,  as  recommended  by  Mr.  Berkeley,  will  answer 
the  same  purpose.  The  fixing  bath  should  be  the  same 
as  above.  When  the  washing  is  complete,  which  will 
take  two  or  three  hours,  the  prints  may  be  toned  if  re- 
quired. A beautiful  brown-black  tone  is  given  by  a weak 
solution  of  ammonium  sulphide,  the  colour  being  per- 
manent. All  excess  should,  of  course,  be  well  washed 
out.  A solution  of  sulphuretted  hydrogen  in  water  will 
answer  the  same  purpose.  Against  the  use  of  such  solu- 
tions we  are  aware  that  many  photographers  will,  meta- 
phorically, hold  up  their  hands,  as  they  will  remember  the 
dread  they  have  of  bringing  any  sulphur  compounds  in 
contact  with  a print  on  albumenized  paper.  They  should 
recollect,  however,  that  the  conditions  are  totally  different. 
It  is  the  organic  compound  of  silver  which  gives  rise  to 
fading,  and  not  the  sulpliuration  of  the  metallic  silver. 
Sulphide  of  silver  is  about  as  permanent  a silver  compound 
as  can  exist,  and  there  can  be  no  danger  of  its  fading. 
Great  care  must  be  taken  to  eliminate  all  traces  of  iron 
salts  by  washing  after  development,  when  using  the 
above  solutions,  otherwise  the  white  will  be  dirty~ 
This  dirty  green  appearance,  however,  may  be  got  rid  of 
by  passing  the  print  through  dilute  hydrochloric  acid. 
The  tone  assumed  by  the  prints  with  this  treatment  is  a 
warm  brown  black,  reaching  a jet  black  if  prolonged. 

An  improvement  in  the  tone  may  also  be  given  by 
using  the  uranium  intensifier  (see  page  207).  Resort 
may  also  be  had  to  gold  and  platinum  toning ; but  the 
above  will  give  almost  every  variety.  If  paper  be  given 
a coating  of  india-rubber  solution,  or  gelatine,  and  then  a 


GELATINIZED  PAPERS. 


219 

coating  of  normal  collodion  (10  grains  of  pyroxyline  to 
1 ounce  of  ether  and  1 ounce  of  alcohol),  the  paper  may 
be  coated  by  turning  up  the  edges  to  form  it  into  a little 
dish,  and  holding  it  on  a glass  plate.  The  emulsion  is 
then  allowed  to  set,  and  eventually  hung  up  to  dry. . 

In  both  methods  of  preparing  the  paper  the  desicca- 
tion takes  place  much  more  rapidly  than  with  a gelatine 
plate,  since  there  are  two  surfaces  by  which  the  drying 
effect  of  the  air  is  utilized. 

F or  direct  enlarged  positives,  the  thinly-coated  paper  is 
extremely  useful,  an  optical  lantern  can  be  used,  and  good 
prints  secured  with  but  very  short  exposure.  As  an 
example  of  the  exposure  necessary  for  this,  we  have  pro- 
duced an  enlargement  of  six  diameters  by  an  exposure 
of  three  minutes  when  using  a triple-wick  oil  lamp  as 
the  source  of  illumination.  It  also  should  take  the  place 
of  collodion  transfers  for  working  upon  in  oils  or 
crayons. 


CHAPTER  XLIII. 


ACETOGELATINE  EMULSIONS. 


De.  H.  W.  Vogel  experimented  in  production  of  emul- 
sions which  should  combine  the  rapidity  of  the  ordinary 
gelatine  plate  with  the  ease  of  coating  of  a collodion 
emulsion.  His  emulsions  are  made  as  follows,  according 
to  the  English  specification  of  his  patent.  He  rightly 
claims  for  himself  the  novelty  of  being  able  to  mix  a solu- 
tion of  pyroxyline  with  one  of  gelatine,  and  thus  getting 
the  advantages  of  both  emulsions.  Any  gelatine  emulsion 
(such  as  that  described,  for  instance,  in  Chap.  XXVII.)  is 
prepared  as  usual,  and  the  pellicle  dried.  This  dried 
emulsion  is  then  dissolved  in  one  of  the  fatty  acids  (such 
as  formic  acetic,  or  propionic  ; acetic  acid,  however,  by 
preference,  on  account  of  its  cheapness).  To  effect  this  it 
is  warmed  in  the  acid,  using  three  to  ten  times  as  much 
acid  as  pellicle.  The  quantity  of  acid  depends  on  the  kind 
of  gelatine  originally  employed.  Sufficient  alcohol  is  now 
added  to  this,  till  it  is  of  proper  consistency  for  flowing 
over  the  plate  when  heated  to  a temperature  of  about  90°  F. 
When  cold  the  emulsion  sets  in  a gelatinous  mass.  Plates 
may  be  coated  with  this  emulsion  per  se : the  emulsion 
is  flowed  over  like  collodion,  and  any  excess  drained  into 
the  bottle.  In  very  hot  weather,  however,  it  is  better  to 
lay  the  plates  flat  for  a short  time,  since  sufficient  emul- 


ACETO-GELATINE  EMULSIONS. 


221 


sion  is  difficult  to  retain  on  the  plate  if  thoroughly  drained. 
In  order  to  give  tenacity,  Dr.  Vogel,  as  before  stated, 
mixes  pyroxyline  with  his  emulsion. 

His  formula  is  this  : — 

Pyroxyline  ...  ...  ...  20  grains 

Acetic  acid  ...  ...  ...  1 ounce 

Alcohol 1 „ 

This  form  of  collodion  is  mixed  with  equal  quantities  of  the 
gelatine  emulsion  just  described.  The  plates  formed  by 
this  collodio-gelatine  emulsion  can  be  used  wet  or  dry. 
Another  method  Dr.  Vogel  describes,  which  is  as  follows. 
Collodion  emulsion  is  prepared  in  the  ordinary  way  (see 
page  45),  and  dried;  70  grains  of  the  pellicle  are  dis- 
solved in  3 ounces  of  alcohol,  and  If  ounce  of  acetic  acid. 
20  grains  of  gelatine  are  dissolved  in  3^  drachms  of  acetic 
acid,  and  added  to  it.  Plates  are  coated  in  the  ordinary 
manner  by  it. 

A plan  which  we  adopted  before  the  publication  of  the 
formula  was  to  take  gelatine  pellicle  (say  50  grains),  dis- 
solve by  aid  of  the  heat  of  hot  water  in  the  smallest 
quantity  of  acetic  acid,  adding  drop  by  drop  till 
the  solution  is  perfect.  Methylated  spirit  was  added  till 
it  flowed  nicely  over  a trial  plate,  when  it  was  filtered 
through  cotton  wool,  washed,  and  was  then  ready  for  use. 
The  plates  must  have  a very  adhesive  substratum ; that 
given  at  page  184  is  effective,  whilst  another  is  [india- 
rubber  in  solution  made  by  dissolving  india-rubber  paste 
in  benzole  till  it  has  the  consistency  of  cream.  There  is 
a tendency,  however,  with  the  latter  for  the  film  to  crack, 
with  the  former  none  whatever. 

The  drawback  to  this  process  is  the  smell  of  the  acetic 
acid,  which  is  decidedly  objectionable.  Again,  too,  it  is  of 
necessity  a more  expensive  process,  since  the  solvents  of 
the  gelatine  are  not  as  common  as  tap  water.  On  the 
other  hand,  the  negatives  obtained  by  it  are  excellent; 
the  gelatine  is  apparently  changed  in  quality,  and  allows 


222 


ACETO-GELATINE  EMULSIONS. 


the  developer  to  permeate  easily,  and  consequently  great 
density  is  obtained.  The  sensitiveness  of  the  emulsion 
is  slightly  diminished  according  to  our  experience,  but 
there  is  a perfect  immunity  from  spots  of  any  description. 
There  is  one  great  convenience  in  this  emulsion,  which  is, 
that  it  can  be  kept  in  a bottle  corked,  and  used  for  coating 
plates  as  required,  instead  of  having  to  coat  more  plates 
than  sometimes  may  be  convenient.  Care  must  be  taken, 
in  coating  the  plates,  that  the  emulsion  does  not  run  into 
ribs.  The  plates  should  be  rocked  as  with  collodion 
emulsion,  and  then  there  is  no  danger  of  this  defect. 

For  developing,  Dr.  Vogel  recommends  the  following  as 
giving  the  best  results  : — 


1 . — Sodium,  mono-carbonate 

(crystalline)  ...  ...  200  grains 

Potassium  bromide...  l£to2  ,, 
Water  ...  ...  ...  £ ounce 


2. — Pyrogallic  acid 
Alcohol 


50  grains 
1 ounce 


3. — Four  parts  of  No.  1 are  mixed  with  one  part  of 
No.  2 for  a normal  exposure.  The  development  must  be 
modified  according  to  circumstances  (see  page  192). 

Dr.  Vogel  also  uses  Nelson’s  developer  (page  198),  and 
the  ferrous  oxalate  (page  235).  In  regard  to  this  latter  he 
uses  it  in  a somewhat  different  form  to  that  given.  His 
formula  is  as  follows : — 


1.  — Potassium  oxalate  (neutral) 

Water  ... 

2. — Potassium  bromide 

Water  ... 

3.  — Hyposulphite  of  soda  ... 

Water  ... 

4.  — Ferrous  sulphate 

Water 


. 10  ounces 
30  „ 

. 12  grains 
. £ ounce 

. 2 grains 

. 1 ounce 

. 1 ounce 

. 3 ounces 


ACETO-GELATINE  EMULSIONS. 


223 


To  develop,  he  mixed 

No.  I 1 £ ounce 

No.  II 15  drops 

No.  IIP 15  „ 

When  well  mixed,  he  adds  ^-ounce  of  No.  4,  and  again 
mixes  and  applies  to  plates. 

M.  Konarzewski  also  gives  a formula  for  a collodio- 
gelatine  emulsion  : — 

Alcohol  *805  2 ounces 

Glacial  acetic  acid  2 „ 

Pyroxyline  18  grains 

To  this  collodion  180  grains  of  gelatine  emulsion  are 
added,  and  dissolved  by  aid  of  heating  in  hot  water.  He 
recommends  a substratum  of  albumen  and  silicate  of 
soda  (page  184). 


* If  the  plates  be  hard,  he  uses  30  drops  of  No.  Ill,  instead  of  15. 


CHAPTER  XL1Y. 


DEFECTS  IN  GELATINE  PLATES. 


Frilling. — What  is  meant  by  frilling  is  the  gelatine 
film  leaving  the  glass  plate  in  folds  or  wrinkles,  and  a 
greater  nuisance  than  this  cannot  be  met  with.  It  is  gene- 
rally met  with  when  fixing  the  plate,  though  we  have 
sometimes  met  with  it  during  the  development,  especially 
in  hot  weather.  We  will  endeavour  to  state  the  causes  of 
frilling  as  they  are  known.  Frilling  is  often  caused  by 
the  use  of  unsuitable  gelatine,  possessing  but  little  tenacity. 
The  more  the  qualities  of  gelatine  are  like  glue  the  less 
chance  there  is  of  meeting  with  this  vexatious  evil.  If 
gelatine,  however,  were  like  glue  in  respect  to  hardness, 
the  difficulty  of  developing  a plate  would  be  very  great, 
since  it  is  too  hard.  To  meet  this  objection,  a certain 
proportion  of  a less  tenacious  gelatine  is  mixed  with  the 
harder  kind,  a very  good  index  of  the  tenacity  being  the 
temperature  at  which  it  melts  after  swelling.  The  addi- 
tion of  chrome  alum  to  an  emulsion  also  prevents  it  to 
a great  extent.  The  objections  to  chrome  alum  are  that 
it  increases  the  tenacity  of  the  gelatine,  and  prevents  easy 
development ; hence  it  should  be  used  sparingly. 

Gelatine  that  has  been  cooked  for  a long  time  has  a 
special  tendency  to  frill,  and,  unless  fresh  gelatine  be 


DEFECTS  IN  GELATINE  PLATES. 


225 


added  to  the  emulsion,  in  some  cases  the  frilling  is  inevit- 
able. Long  cooking  (in  warm  weather  particularly) 
means  decomposition  of  the  gelatine,  and  decomposed 
gelatine  is  very  detrimental  in  preparing  a dry  plate. 
Boiling  for  a short  time  has  much  the  same  effect  on 
the  gelatine  as  cooking  at  a lower  temperature  ; hence, 
to  avoid  frilling,  it  is  better  on  the  whole  not  to  boil  the 
emulsion  with  the  full  amount  of  gelatine. 

Another  source  of  frilling  is  the  plate  being  improperly 
cleaned.  If  water  will  not  flow  in  a uniform  sheet  from  a 
plate,  it  may  be  well  understood  that  there  will  be  but  little 
adhesion  between  it  and  an  aqueous  solution  of  gelatine 
(see  page  182).  This  we  believe  to  be  one  fruitful  source 
of  the  evil. 

Another  source  of  frilling  is  unequal  drying.  Thus, 
if  plates  be  dried  in  an  unventilated  box,  it  will  usually 
be  found  that  a central  patch  refuses  to  dry  till  long  after 
the  outsides  are  completely  desiccated.  At  the  junction 
of  this  central  patch  with  the  neighbouring  gelatine 
frilling  is  to  be  looked  for.  It  will  spread  to  the  parts 
which  have  been  the  longest  in  drying.  This  is  due  to  a 
false  tension  set  up  in  the  film,  and  can  only  be  conquered 
by  drying  the  plate  by  means  of  alcohol,  or  by  using  a 
proper  drying  cupboard. 

Again,  when  plates  are  coated  in  hot  weather,  unless 
precautions  as  innumerated  in  Chap.  XXXIII.  are  taken, 
they  take  long  to  set.  The  emulsion  remains  liquid  on 
the  plate  for  sufficient  time  to  allow  the  heavier  particles 
of  silver  bromide*  to  settle  down  on  the  surface  of  the  glass. 
This  of  course  diminishes  the  surface  to  which  adhesion 
can  take  place.  W e believe  that  1 1 t ost  of  the  frilling  which 
takes  place  in  plates  prepared  in  hot  weather  may  be 
traced  to  this  cause.  When  washing  after  fixing,  frilling 
is  often  caused  by  allowing  a stream  of  water  from  the 


* This  is  particularly  liable  to  happen  when  the  emulsion  has  been  long 
boiled  or  carelessly  mixed. 


226 


DEFECTS  IN  GELATINE  PLATES. 


tap  to  impinge  on  the  plate.  This  should  never  he 
allowed  if  the  film  is  at  all  delicate. 

At  page  147  it  has  already  been  stated  that  chrome 
alum  is  used  with  a gelatine  emulsion.  This  is  recom- 
mended to  prevent  frilling  when  soft  gelatine  is  used  in 
hot  weather.  Plates  which  frill  or  blister  will  not  show 
any  signs  of  so  doing  if  kept  for  a few  months. 

A general  remedy  for  frilling  is  to  coat  the  plate  with 
normal  collodion  containing  about  six  grains  of  tough 
pyroxyline  to  the  ounce  of  solvents.  The  formula  would 
be  thus : — 

Tough  pyroxyline  ...  ...  6 grains 

Alcohol  (*820)  ...  ...  ounce 

Etlier  (.725)  % „ 

This  may  he  applied  to  the  film  immediately  before 
developing  the  plate  ; the  solvents  are  washed  away  in  a 
dish  of  clean  water  first,  and,  when  all  repellent  action  is 
gone,  the  developing  solutions  applied.  If  the  film  has 
been  allowed  to  dry,  a solution  of  one  part  of  ether  to  three 
of  alcohol  will  render  it  pervious  to  the  developing 
solutions.*  In  some  batches  of  plates  frilling  is  so  obsti- 
nate that,  although  collodion  be  applied,  the  film  has  a 
tendency  to  curl  off  from  the  edges  of  the  plate.  It  is 
advisable,  when  such  is  suspected,  to  run  a brush  with  an 
india-rubber  solution  round  the  edges,  to  prevent  the 
water  having  access  to  that  part  of  the  film.  When  fixing 
such  plates  it  not  unfrequently  happens  that  blisters 
appear,  and,  if  allowed  to  remain  as  they  were,  will  spoil 
the  negative.  To  avoid  this,  we  wash  the  plate  under 
the  tap  till  all  the  blisters  join,  and  the  film  presents  the 
appearance  of  a sack  containing  water.  A prick  at  one 
corner  of  the  plate  lets  this  liquid  free,  and  the  washing 
can  take  place  as  usual.  The  obstinate  cases  of  frilling 
usually  occur  through  plates  being  prepared  in  very  hot 


* We  have  found  this  essential  in  intensifying  negatives  which  have  been 
treated  with  collodion  after  fixing  and  drying. 


DEFECTS  IN  GELATINE  PLATES. 


227 


weather,  and  the  film  being  dried  without  first  setting. 
Another  palliative  is,  in  development,  to  use  a mixture  of 
half  alcohol  and  half  water,  in  which  to  dissolve  the  pyro- 
gallic  acid,  using  twice  the  amount  to  each  ounce  to  that 
usually  employed.  This  extra  pyrogallic  acid  is  required, 
as  the  developer  turns  black  sooner  in  consequence  of 
using  the  alcohol.  If  this  stops  frilling  during  develop- 
ment, but  frilling  takes  place  during  fixing,  the  plate 
should  next  be  immersed  in  a strong  alum  bath  (see 
page  209)  for  a few  seconds,  be  very  carefully  rinsed  with 
water,  and  then  set  up  to  dry.  When  once  dry,  it  may  be 
fixed  without  any  risk.  A more  expensive  method  is  to 
add  to  the  hyposulphite  bath  as  much  methylated  spirit  as 
it  will  bear  without  precipitating  the  salt. 

Some  writers  state  that,  by  immersing  the  plate  in  a 
saturated  solution  of  Epsom  salts,  frilling  is  avoided  : we 
have  not  succeeded  ourselves  in  proving  its  universal 
efficacy. 

Blisters  on  the  Film. — Blisters  on  a film  are  the  usual 
preliminaries  to  frilling.  When  they  commence,  further 
damage  may  usually  be  avoided  by  flooding  the  plate 
with  methylated  spirit.  This  extracts  the  water,  and 
with  it  any  soluble  salt  that  may  be  left,  and  the  plate 
speedily  dries,  which  is  an  advantage  if  it  be  fixed. 
Blisters  are  usually  found  to  follow  the  rubbing  marks 
of  the  polishing  cloth,  if  such  be  used.  The  cure  here 
is  self-evident.  They  also  are  to  be  found  in  places 
between  which  the  film  has  dried  quickly  and  slowly. 

Red  Fog. — The  writer  fortunately  knows  very  little 
about  this  disaster,  but  it  is  found  to  occur  if  the  silver 
nitrate  is  in  excess  of  the  salts  with  which  it  should 
combine.  Cyanide  will  sometimes  eliminate  it  from  a 
film*  but  this  remedy  must  be  used  with  caution. 

Green  Fog. — This  fog  is  due  to  decomposed  gelatine 
and  oxidized  pyrogallic  acid.  Green  by  reflected  light, 
it  is  pink  by  transmitted  light,  being  dichroic.  This  at 
once  points  to  the  fact  that  this  fog  is  somewhat  of  the 


228 


DEFECTS  IN  GELATINE  PLATES. 


nature  of  a dye,  and  every  oxidizing  agent  ought  to 
destroy  it.  In  some  cases  we  have  immersed  the  film  in 
a strong  solution  of  bichromate  of  potash,  and  on  after- 
wards washing,  the  fog  has  disappeared;  hut  whether 
it  is  a certain  cure,  we  hesitate  to  say ; it  is,  at  any  rate, 
worth  trying. 

General  Fog. — By  general  fog  we  mean  the  fog  pro- 
duced during  development,  and  is  caused  by  the  partial 
reduction  of  the  silver  salt  all  over  the  film.  This  is  pro- 
bably due  to  the  decomposition  of  the  gelatine  by  long 
cooking,  the  products  of  which  in  the  presence  of  a 
developer  are  apt  to  react  on  the  silver  salt,  and  produce 
a partial  reduction  in  it.  The  production  of  this  kind 
of  fog,  and  electrical  disturbance  in  the  atmosphere,  are 
apt  to  go  together.  In  unfavourable  weather,  a few 
drops  of  a saturated  solution  of  salycic  acid  should  be 
added  to  the  gelatine  during  boiling  or  prolonged 
emulsification  ; this  will  generally  check  or  entirely  pre- 
vent the  decomposition.  An  excess  of  silver  is  likewise 
very  likely  to  produce  the  evil,  but  the  presence  of  iodide 
in  the  emulsion  will  almost  certainly  cure  it.  Another 
fruitful  source  of  fog  is  the  light  admitted  to  the  plates 
during  preparation  or  development.  The  light  should  be 
tested  by  putting  a plate  in  the  dark  slide,  and  drawing 
up  half  the  front,  and  exposing  the  half-plate  to  the  light 
for  ten  minutes.  If  the  fog  be  due  to  this  cause,  the 
plate  on  development  is  sure  to  show  it  by  an  increased 
reduction  of  metallic  silver  in  the  part  so  exposed. 

Whatever  may  be  the  cause  of  fog — whether  the  emul- 
sion itself  be  in  fault,  or  whether  the  plates  have  seen 
light — we  have  found  that,  as  in  the  collodio-bromide 
process,  there  is  one  certain  sure  cure.  If  the  emulsion 
be  at  fault,  squeeze  it  into  water  (see  page  25)  containing 
10  grains  of  potassium  bichromate  to  each  ounce,  and 
allow  it  to  rest  for  an  hour,  and  then  wash  again  for  a 
couple  of  hours  more.  If  all  the  bichromate  be  not  taken 
out  by  this  washing,  it  is  not  of  much  consequence,  since 


DEFECTS  IN  GELATINE  PLATES. 


229 


when  dry  it  is  inactive.  The  sensitiveness  after  this  treat- 
ment is  not  much  diminished,  and  the  negatives  taken 
with  it  are  beautifully  bright.  Plates  may  be  treated  in 
precisely  the  same  manner,  and  give  unveiled  pictures. 
There  is  a slight  diminution  of  sensitiveness  if  the  bichro- 
mate be  not  at  all  washed  out,  but  nothing  to  hurt  except 
where  very  great  rapidity  is  required. 

Another  cure  is  the  addition  of  a few  grains  of  cupric 
chloride.  This  diminishes  the  sensitiveness  slightly,  but 
is  most  effectual,  the  negatives  yielding  bright  and  bril- 
liant images.  A remarkable  fact  about  the  addition  of  the 
cupric  chloride  is,  that  the  grey  form  of  bromide  is  con- 
verted into  the  red  form  if  much  of  the  copper  salt  be 
employed.  The  addition  of  a few  grains  of  ferricyanide 
of  potassium  with  a little  bromide  of  potassium  (see 
page  13)  is  also  a perfect  cure,  but  this  slows  the  emulsion. 

Another  method  is  to  add  a few  drops  of  hydrochloric 
acid  to  the  emulsion,  or  to  slightly  acidify  the  first  wash 
water  with  it  • about  1 drachm  to  a pint  of  water  is  gene- 
rally ample.  The  length  of  time  which  the  emulsion 
should  be  in  contact  with  the  acidified  water  depends  on 
the  size  of  the  mesh  of  the  canvas  through  which  the 
emulsion  is  squeezed.  For  a medium  size,  half  an  hour 
suffices.  The  emulsion  has  a tendency  to  become  in- 
soluble by  this  method. 

Flatness  of  Image  is  usually  due  to  over-exposure  and 
development  with  the  alkaline  developer : the  use  of 
ferrous  oxalate  mitigates  the  evil,  whilst  if  iodide  be  in 
the  film,  we  have  never  found  any  great  lack  of  density 
to  arise.  Feebleness  of  the  image  is  also  often  caused 
by  too  thin  a coating  of  emulsion.  In  our  own  experi- 
ence, a thick  film  is  a desideratum,  giving  all  the  neces- 
sary density  to  the  image  with  facility.  Remember  that 
when  a vigorous  image  is  required,  it  is  most  readily 
obtained  by  using  a freshly  prepared  and  strong  ferrous 
oxalate  solution  (see  page  235). 

rl  oo  great  Density  of  Image  is  sometimes  met  with,  and 


230 


DEFECTS  IN  GELATINE  PLATES. 


can  be  remedied  by  applying  ferric  chloride  to  the  film, 
and  then  subsequently  immersing  in  the  hyposulphite  of 
soda  fixing  bath. 

The  formula  recommended  is — 

Ferric  chloride...  ...  ...  1 drachm 

Water  ...  ...  ..  ...  4 ounces. 

This  is  flowed  over  the  plate  a short  time,  and  then,  after 
washing,  the  plate  is  immersed  in  the  fixing  bath.  The 
solution  acts  very  vigorously,  and  should  be  diluted  if 
only  a small  reduction  is  required.  Local  reduction  may 
be  effected  by  using  a paint  brush  charged  with  this 
solution  on  the  moistened  film.  This  practice  is  not,  how- 
ever, much  to  be  commended,  as  it  is  rather  working  in 
the  dark. 

Density  may  also  be  diminished  by  the  use  of  a strong- 
solution  of  cyanide.  Local  reduction  may  be  given  by 
moistening  the  parts  required  to  be  reduced  with  water 
by  a paint  brush,  and  then  applying  the  cyanide  in  the 
same  manner.  The  reduction  can  be  seen  progressing. 

There  are  a variety  of  formulas  extant  for  reducing 
negatives.  Perhaps  the  best  is  eau  de  javelle,  which  can 
be  obtained  of  all  chemists,  but  which  is  made  as  follows : 

Dry  chloride  of  lime  ...  ...  2 ounces 

Carbonate  of  potash  ...  ...  4 ,, 

Water  ...  ...  ...  ...  40  „ 

The  lime  is  mixed  with  30  ounces  of  the  water,  and  the  car- 
bonate dissolved  in  the  other  10  ounces.  The  solutions  are 
mixed,  boiled,  and  filtered.  The  filtered  solution  should 
be  diluted,  and  the  plate  immersed  in  it  till  reduction  takes 
place.  The  plate  should  be  fixed,  and  again  washed. 

Yellow  Stains. — Usually  a yellowish  veil  appears  to 
dim  the  brightness  of  the  shadows  when  the  development 
has  been  effected  by  the  alkaline  developer.  This  may 
be  removed,  if  thought  requisite,  by  the  application  of 
one  or  two  drops  of  hydrochloric  acid  to  an  ounce  of 


DEFECTS  IN  GELATINE  PLATES. 


231 


water,  and  floating  it  over  the  surface  of  the  plate.  The 
film  must  he  washed  almost  immediately,  as  the  acid  is  apt 
to  cause  frilling. 

Another  formula,  due  to  Mr.  J.  Cowell,  is  to  immerse 


e plate  in — 

Alum 

• • • 

...  2 ounces 

Citric  acid 

• • • 

...  1 ounce 

Water  ... 

... 

...  10  ounces. 

Another  formula  is — 

Saturated  solution  of  alum 

...  20  ounces 

Hydrochloric  acid 

... 

...  J ounce 

The  negative  should  he  well  washed  in  all  cases  after  the 
application  of  either  of  them. 

loo  Granular  an  Emulsion  is  usually  due  to  had  mixing 
of  the  soluble  bromide  and  the  silver  nitrate,  hut  it  may 
also  he  caused  hy  over-hoiling,  and  also  hy  too  small  a 
quantity  of  gelatine  in  the  boiling  operation.  Digesting 
too  long  with  ammonia,  as  in  Van  Monckh oven’s  process, 
has  the  same  effect.  There  is  no  cure  for  this  evil. 

Opaque  Spots  on  a plate  are  almost  invariably  due  to 
dust  settling  on  the  film  when  drying ; they  also  may  he 
due  to  imperfect  filtering  of  the  emulsion. 

Semi-transparent  Spots  on  the  plate  before  development 
are  generally  due  to  (1st)  excrescences  on  the  glass  plate, 
or  (2nd)  to  the  use  of  gelatine  containing  grease. 

As  has  already  been  pointed  out  on  page  135,  certain 
gelatines  are  apt  to  contain  grease,  and  that  so  intimately 
that  soaking  in  ether  or  washing  with  ammonia  will  not 
eliminate  it.  A specific  is  as  follows  : — We  will  suppose 
that  80  grains  of  Coignet’s  gelatine  are  required : 
90  grains  are  weighed  out,  soaked  in  water,  drained,  and 
melted.  The  liquid  is  then  very  slowly  poured,  almost 
drop  hy  drop,  into  methylated  spirit,  free  from  resin, 
where  it  is  precipitated  in  shreds  of  a white  pasty 
character ; after  it  is  all  precipitated  the  spirit  is  poured 


232 


DEFECTS  IN  GELATINE  PLATES. 


off,  and  a slight  rinse  with  fresh  spirit  given,  and  then  it 
is  covered  with  water,  in  which  it  should  remain  till  the 
whiteness  disappears.  The  water  should  then  be  changed, 
and  the  gelatine  drained  and  redissolved  ; about  10  grains 
out  of  the  90  seem  to  be  dissolved  in  the  mixture  of 
alcohol  and  w’ater.  Emulsions  made  with  this  gelatine 
will  be  markedly  free  from  grease  spots.  The  same 
method  may  be  adopted  for  large  quantities  of  gelatine, 
omitting  the  final  wash  with  water,  and  leaving  it  to  dry 
spontaneously.  This  is  best  done  on  glazed  dishes.  The 
gelatine  can  be  broken  up,  weighed,  and  used  in  the 
usual  manner. 

Dull  Spots  on  the  Negative  are  also  due  to  the  use  of 
gelatine  which  contains  greasy  matter. 

Want  of  Density  in  a negative  may  be  caused  by  over- 
exposure (see  page  229),  but  it  more  often  arises  from 
the  emulsion  itself.  A rapid  emulsion  will  always  give  a 
feebler  image  than  a slow  emulsion,  although  to  form  the 
image  the  same  amount  of  silver  may  be  reduced.  This 
shows  that  the  silver  is  in  such  a state  of  aggregation 
that  it  does  not  possess  what  may  be  called  covering- 
powers.  We  have  found  that  the  addition  of  a chloride 
emulsion  materially  aids  the  production  of  density.  If 
one-fifth  part  of  an  emulsion  prepared  according  to 
Chapter  XLI.  be  added  to  an  emulsion  lacking  in  density- 
giving qualities,  it  will  be  secured  without  detriment  to 
the  sensitiveness.  The  range  of  sensitiveness  will  be 
slightly  altered  (see  page  241).  A hard  gelatine  is  also 
conducive  to  feeble  images.  If  prepared  plates  give 
feeble  images,  resort  must  be  had  to  intensifying. 


APPENDIX. 


A Liebig's  Condenser  is  a very  useful  piece  of  apparatus 
for  rectifying  alcohol  and  distilling  emulsion,  but  it  re- 
quires certain  precautions  to  be  taken  to  ensure  safety. 
The  apparatus  arranged  as  in  fig.  16  is  suitable  for  the 
purpose. 

The  condenser  consists  of  two  parts  : first,  a straight 
glass  tube  (5),  bent  at  the  ends,  to  which  the  flask  is 
attached ; the  second,  a jacket  (c)  surrounding  the  bulk 
of  the  tube  as  shown  in  the  figure.  The  jacket  has  two 


short  tubes  ( d and  e)  connected  with  it,  d being  that 
through  which  the  cold  water  is  supplied  to  the  jacket, 
and  e that  through  wdiich  the  warm  water  is  forced  out. 
A couple  of  india-rubber  corks  are  bored  to  fit  the  central 


234 


APPENDIX. 


tube  and  to  close  the  ends  of  the  larger  tubes.  The  con- 
denser can  be  held  by  a clamp,  B.  The  cold  water  can 
be  supplied  from  a water  tap,  a pinch-cock  being  used 
on  the  india-rubber  tube  from  c?,  so  as  to  allow  a very 
small  flow  ; or  it  may  be  supplied  from  a jar  with  a 
syphon  arrangement,  if  care  be  taken  to  keep  the  bottom 
of  the  vessel  above  the  highest  end  of  the  jacket.  For 
distilling  alcohol  or  an  emulsion,  the  flask  should  be  held 
in  a metal  bowl,  C,  filled  with  water,  but  the  bottom  of  the 
flask  should  not  touch  the  bottom  of  the  bowl,  otherwise 
there  is  danger  of  bumping  and  fracture  of  the  former.  In 
practice,  we  have  found  that  the  ring  formed  by  blotting- 
paper  is  sufficient  protection  to  the  flask.  This  is  placed 
in  the  bowl,  and  the  flask  placed  upon  it.  A jacket  may 
surround  the  source  of  heat,  which  may  be  a spirit-lamp, 
a gas  jet,  or  an  oil  lamp,  but  is  unnecessary  when  there  is 
no  draught  in  the  place  where  the  distillation  is  being 
carried  on.  The  alcohol  distils  over,  and  is  condensed 
in  the  tube  5,  and  drops  into  the  flask  D.  It  is  not  abso- 
lutely necessary  that  the  flask  should  not  come  in  contact 
with  the  flame  of  the  source  of  heat,  but  it  is  safer  not  to 
allow  it  to  do  so. 

If  we  have  alcohol  of  (say)  *830  specific  gravity  (a 
very  common  one,  by-the-bye)  and  we  wish  to  rectify 
it,  the  best  method  is  to  place  in  the  bottle  containing  it 
sufficient  freshly  burnt  unslaked  lime  to  completely 
saturate  the  spirit,  leaving,  in  fact,  very  little  liquid 
above  the  sediment ; after  standing  two  or  three  days 
this  mass  must  be  put  in  retort,  and  the  distillation 
proceeded  with.  The  distilled  spirit  will  be  found  to  be 
of  a specific  gravity  of  *795.  An  anhydrous  spirit  of  this 
specific  gravity  is  very  useful  to  have  in  stock,  as  it 
enables  water  to  be  used  in  the  operations  of  making 
emulsions  without  exposing  the  film  to  the  evil  of  crapi- 
ness.  The  spirit  may  be  distilled  till  the  lime  appears 
quite  dry,  for  the  latter  will  hold  the  water  in  combination 
at  a temperature  far  beyond  the  boiling  point  of  water. 


APPENDIX. 


235 


If  spirit  be  distilled  from  alcohol  containing  about 
half  as  much  lime  as  indicated  above,  it  will  be  found 
that  the  specific  gravity  of  the  distillate  will  be  about 
*812,  which  is  a very  convenient  mixture  of  alcohol  and 
water. 


Organic  Iron  Developers. 

Simple  form  of  F errous-oxalate  Developer. — A saturated 
solution  of  the  neutral  potassium  oxalate  is  first  prepared. 
A crystal  of  oxalic  acid  is  next  added,  to  prevent  the 
slightest  trace  of  alkalinity.  At  one  time  we  used  to  add 
ferrous  oxalate  to  a boiling  potassium  oxalate  solution, 
only  so  much  of  the  oxalate  being  added  as  to  leave  a 
slight  portion  of  the  ferrous  compound  undissolved.  We 
prefer  now  to  add  the  ferrous  oxalate  to  the  cold  satu- 
rated solution  of  the  potassium  salt,  and  to  allow  them 
to  remain  in  contact  with  one  another  for  twenty-four 
hours,  shaking  occasionally.  The  clear  solution  can 
be  decanted  off.  This  method  prevents  the  deposition  of 
crystals  on  the  sides  of  the  bottles,  which  always  are 
deposited  if  the  ferrous  oxalate  be  heated  with  the 
potassium  oxalate.  The  solution  will  be  of  a deep  red 
colour. 

The  ferrous  oxalate  solution  rapidly  oxidizes  by  con- 
tact with  the  air,  as  already  hinted  at,  and  our  own  prac- 
tice is  to  fill  4-ounce  bottles  with  it,  cork  them  up,  and 
then  to  lute  the  corks  with  solid  paraffin.  Mr.  Warnerke 
has  a still  better  plan.  He  uses  a stoppered  bottle  having 
an  opening  near  the  bottom,  such  as  can  be  procured  at 
any  chemical  dealer’s.  Into  this  opening  he  fits  a cork 
carrying  a small  glass  tube  ; on  to  the  end  of  this  (out- 
side the  bottle,  of  course)  he  fits  a piece  of  india-rubber 
tubing,  and  connects  this  with  a similar  piece  of  bent 
glass  tubing,  which  reaches  nearly  as  high  as  the  top  of 
the  bottle.  He  fills  the  bottle  two-thirds  way  up  with 
the  ferrous  oxalate  solution,  and  then  pours  in  a layer  of 
liquid  paraffin.  This  prevents  any  access  of  air  to  the 


2 36 


APPENDIX. 


solution.  To  get  at  the  solution,  the  bent  tube  is  turned 
down  below  the  level  of  the  paraffin,  and  the  developing 
cup  or  bottle  filled. 

Dr. Eder's  Ferrous  Oxalate . — Mr.  York,  working  on  the 
directions  of  Dr.  Eder,  gives  the  following  formula  : — 

No.  1. 

Ferrous  sulphate  ...  ...  160  grains 

Water  ...  ...  ...  ...  1 ounce 

No*  2. 

Potassium  oxalate  (neutral)  ...  1 ounce 

Water  ...  ...  ...  ...  3 ounces 

This  makes  up  4 ounces  of  developer,  and  by  using  these 
quantities,  saturated  solutions  are  obtained.  Personally, 
we  prefer  4 parts  of  No.  1 to  1 of  No.  1. 

Strong  Ferrous  Oxalate  Developer  prepared  with  Ferrous 
Sulphate. — A still  stronger  form  of  ferrous  oxalate  deve- 
loper can  be  made  by  taking  a saturated  solution  of  potas- 
sium oxalate  and  adding  to  it  crystals  of  ferrous  sulphate. 
These  must  be  added  cautiously,  since  part  of  the  potas- 
sium oxalate  is  converted  into  ferrous  oxalate,  and  the 
remainder  holds  it  in  solution. 

Mr.  York’s  formula  for  the  potassium  oxalate  may  be 
taken,  and  to  it  200  grains  of  sulphate  of  iron  be  added 
(powdered  up  in  a mortar  by  preference).  It  wrill  pro- 
bably be  found  that  some  of  the  yellow  oxalate  will  pre- 
cipitate, in  which  case  crystals  of  potassium  oxalate  must 
be  added  to  the  solution  till  such  precipitate  is  re- 
dissolved. 

Ferrous  Citrate  Developer. — The  following  is  the  method 
of  making  ferrous  citrate  developer  according  to  Dr. 
Eder  and  Capt.  Pizzighelli’s  plan  : — 600  grains  of  citric 
acid  are  dissolved  in  4-J  ounces  of  water  with  the  aid  of 
heat,  and  exactly  neutralized  with  ammonia ; 400  grains 
of  citric  acid  are  then  added,  and  the  bulk  of  the  fluid 
made  up  to  9 ounces  of  water ; 3 drachms  of  this  solution 


APPENDIX. 


237 


are  mixed  with  1 drachm  of  a saturated  solution  of  ferrous 
sulphate  and  12  minims  of  a solution  of  sodium  chloride 
(30  grains  to  the  ounce  of  water). 

Ferrous  citrate  may  he  purchased  and  dissolved  in  a 
saturated  solution  of  ammonium  citrate,  adding  citric  acid 
if  required  to  give  a clear  picture. 

F errous-Citro-  Oxalate. — This  developer,  introduced  by 
the  writer,  is  made  as  follows  : — 

Potassium  citrate  (neutral)  ...  100  grains 
Ferrous  oxalate  ...  ...  22  „ 

Water  ...  ...  ...  ...  1 ounce 

The  potassium  citrate  is  first  dissolved  in  a flask  by  heat, 
and,  when  nearly  boiling,  the  ferrous  oxalate  is  added,  and 
shaken  up  in  it,  a cork  being  used  to  prevent  the  access  of 
air  to  it.  This  quantity  of  ferrous-oxalate  should  just 
dissolve.  It  may  be  cooled  by  allowing  cold  water  to 
flow  over  it,  and  should  then  have  a citrony-red  colour. 

A weaker  solution  is  made  the  same  way  with  the 
following  formula : — 

Potassium  citrate  ...  ...  50  grains 

Ferrous  oxalate  .. . ...  ...  12  „ 

Water  ...  ...  ...  ...  1 ounce 

These  solutions  keep  well  when  corked  up  in  bottles. 
There  is  no  deposit  from  keeping  even  when  oxidized, 
which  is  shown  by  the  solution  turning  an  olive  green 
colour. 

HydroMnone  Developer. — This  developer  being  expen- 
sive at  the  present  time,  it  is  merely  placed  in  this  work 
for  reference.  It  has  a slightly  great tr  developing  power 
than  pyrogallic  acid.  To  make  a normal  developer — 

No.  1. 

Hydrokinone  ...  ...  6 to  12  grains 

Water  ...  ...  ...  ...  1 ounce. 

No.  2. 

Carbonate  of  ammonia  in  water  ...  A saturated  solution. 
To  every  ounce  of  No.  1 use  1 drachm  of  No.  2. 


238 


APPENDIX. 


On  Intensifying  Gelatine  Negatives  with  Silver  before 
Fixing. — The  great  danger  in  intensifying  gelatine  plates 
after  fixing  are  red  stains,  and  this  has  usually  been  attri- 
buted to  the  fact  that  hyposulphite  is  left  in  the  film.  In 
Chapter  XL.  it  has  been  shown  how  this  salt  can  be 
decomposed,  but  with  some  the  same  stains  occur,  even 
when  it  is  so  altered.  The  same  may  be  said  when  intensi- 
fying gelatine  plates  before  fixing,  when  no  hyposulphite 
has  been  used.  After  some  experimentation,  the  writer  has 
been  forced  to  the  conclusion  that  certain  gelatines,  when 
boiled,  decompose  into  some  compound  which  is  liable 
to  combine  readily  with  silver,  and  that  it  is  this  body 
which,  in  reality,  is  often  the  cause  of  the  stains.  Plates 
prepared  with  an  emulsion  which  has  not  been  boiled  can 
usually  be  intensified  both  before  and  after  (when  all  the 
hyposulphite  has  been  eliminated)  fixing  without  any 
staining  whatever.  In  the  case  of  these  films  the  former 
condition  is  the  better  in  which  to  give  intensity.  The 
plan  to  adopt  when  using  boiled  emulsions  is  to  immerse 
the  plate  in  alum  (or  chrome  alum),  rinse,  and  dry 
thoroughly,  and  then  intensify.  By  this  procedure  the 
film  is  not  penetrated  by  the  intensifying  solutions,  and 
consequently  any  stain,  if  there  be  any,  is  a surface  stain, 
which  can  be  immediately  eliminated  by  a weak  solution 
of  cyanide. 

Intensifying  Solutions. — The  following  is  a good  standard 
intensifier  for  both  collodion  and  gelatine  plates  : — 


Pyrogallic  acid 

No.  1. 

2 

grains 

Citric  acid 

• • • 

...  2 

Water  ... 

... 

...  1 

ounce. 

Silver  nitrate  . . . 

No.  2. 

...  20 

grains 

Water  ... 

... 

...  1 

ounce. 

To  intensify,  to  every  ounce  of  No.  1,  20  drops  of  No.  2 


APPENDIX. 


239 


should  be  added.  It  is  well  to  flow  No.  1 over  the  plate 
first , and  then  to  drop  No.  2 into  the  cup  and  return 
No.  1 on  to  it.  The  solution  gradually  gets  a dark  colour ; 
but  as  long  as  it  is  perfectly  clear  it  may  be  used  with 
impunity.  Directly  a precipitation  of  metallic  silver  is 
observed,  fresh  solution  should  be  mixed. 

Slow  Collodion  Emulsion  Process  for  transparencies. — 
The  following  formula  has  met  with  approval  for  the  pre- 
paration of  a collodion  emulsion  for  transparencies,  and 
was  one  which  we  used  for  producing  intense  negatives  : 
50  grains  of  silver  nitrate  are  dissolved  in  -J-  drachm  of 
water,  and  J ounce  of  boiling  alcohol  (*805)  added.  This 
is  poured  on  10  grains  of  pyroxyline,  and  then  1 ounce  of 
ether  added  to  dissolve  the  cotton.  The  silver  veiy  pro- 
bably will  precipitate  in  very  fine  grains,  but  this  is  of 
no  consequence.  In  another  J ounce  of  alcohol,  40  grains 
of  zinc  bromide  are  dissolved,  and  this  solution  is  gradu- 
ally added  to  the  above  collodion  with  shaking.  Such 
an  emulsion  will  be  found  perfectly  free  from  ’mottling 
caused  by  excess  of  water,  and  will  flow  smoothly. 
When  a plate  is  coated,  it  is  washed,  and  any  preserva- 
tive used  (preferably  beer),  to  which  to  every  \ pint  a 
lump  of  sugar  of  the  size  of  a large  hazel  nut  is  added. 

Slow  Gelatine  Emulsion. — Slow  gelatine  emulsion  may 
be  prepared  by  the  formula  given  in  Chap.  XXXVII.,  by 
reducing  the  time  of  boiling  to  five  minutes.  If  emulsi- 
fication, as  described  in  Chap.  XXXVI.,  be  accepted,  it 
will  be  found  that  after  twelve  hours  it  will  be  in  a con- 
dition to  give  a slow  plate.  Any  emulsion  may  be  made 
slow  by  adding  10  grains  of  copper  chloride  to  it  after 
boiling.  These  slow  plates  give  wonderful  density. 

Backing  for  Gelatine  Plates. — It  will  be  found  that,  with 
most  gelatine  plates,  blurring  is  a very  frequent  occurrence 
if  the  exposure  be  at  all  prolonged.  This  blurring  can 
be  nearly  got  rid  of  by  the  use  of  a backing  in  optical 
contact  with  the  back  of  the  plate.  The  amount  ot 
blurring  that  may  be  expected  can  be  judged  by  placing 


240 


APPENDIX. 


the  film  side  of  the  plate  against  printed  matter,  and 
seeing  with  what  degree  of  distinctness  it  can  he 
read. 

At  page  84  a formula  for  hacking  collodion  plates  was 
given,  hut  for  gelatine  plates  it  is  as  well  to  have  some 
material  which  is  soluble  in  alcohol  rather  than  in  water, 
for  very  evident  reasons.  There  is  nothing  better  than 
asphaltum  dissolved  in  benzine,  and  this  remains  intact 
during  development,  and  can  he  removed  with  a little 
turpentine  or  benzine  afterwards.  Another  plan  is  to 
dissolve  aurine  in  collodion,  and  coat  the  hack  of  the  plate 
with  this.  Water  will  readily  remove  the  film. 

Recovery  of  Residues. — The  residues  from  gelatine  emul- 
sions may  he  recovered  by  two  methods.  First,  by  adding 
l-10th  part  of  its  hulk  of  a saturated  solution  of  caustic 
potash  or  soda,  and  then  boiling.  This  precipitates 
the  silver  in  the  metallic  state,  and  kills  the  viscosity  of 
the  gelatine.  The  solution  eventually  becomes  colour- 
less, and  the  black  deposit  left  contains  all  the  metallic 
silver.  This  may  be  dried,  burnt  slightly  at  a red  heat, 
and  treated  with  nitric  acid,  and  fresh  silver  nitrate  pro- 
cured ; or  it  may  be  added  direct  to  the  other  residues 
(old  films,  whether  of  collodion  or  gelatine,  may  be 
similarly  treated). 

The  second  method  is  to  add  half  an  ounce  of  hydro- 
chloric or  sulphuric  acid  to  each  ten  ounces  of  emulsion, 
and  to  boil.  The  acid  destroys  the  gelatine,  and  the  silver 
bromide  and  iodide  precipitate  at  the  bottom  of  the  glazed 
saucepan  or  vessel  in  which  it  may  have  been  boiled. 
After  decanting  the  supernatant  fluid,  the  precipitate  is 
added  to  the  residues  for  reduction. 

Coloured  Medium  for  Windows. — Mr.  Warnerke  has 
adopted  an  admirable  material  for  colouring  windows.  It 
is  simply  the  ruby-coloured  cloth  used  by  bookbinders. 
When  examined  by  the  spectroscope,  two  thicknesses 
are  found  to  do  away  with  every  trace  of  blue,  leaving 
behind  merely  a band  of  red.  The  price  is  ridiculously 


APPENDIX. 


241 


low  compared  with  most  materials  used,  and  we  can 
recommend  it  to  onr  readers. 

Effect  of  Mixtures  of  the  Haloids. — Since  the  earlier  parts 
of  this  book  were  put  in  type,  the  writer  has  made  a series 
of  investigations  into  the  effect  of  mixtures  of  iodide  and 
bromide,  iodide  and  chloride,  bromide  and  chloride,  and 
all  these  haloid  silver  salts.  As  a result,  he  finds  that 
when  mixtures  of  iodide  and  bromide  or  iodide  and 
chloride  are  used,  that  a secondary  action  is  set  up  by 
the  liberation  of  the  iodine,  chlorine,  and  bromine,  and 
that  a new  molecule  is  formed  which  is  a true  double 
salt.  This  double  salt  is  more  sensitive  to  the  blue  than 
it  is  to  the  violet ; hence,  by  using  a large  part  of  iodide 
(say  £)  with  bromide,  it  is  possible  to  make  emulsions 
which  shall,  we  believe,  render  landscapes  better  than  the 
ordinary  bromide  alone.  The  addition  of  a small  quan- 
tity of  iodide  is  at  all  times  advisable  on  this  account. 
F or  further  particulars  of  this  investigation,  the  reader  is 
referred  to  the  Proceedings  of  the  Royal  Society,  No.  217, 
Yol.  XXXIII. 

Plates  prepared  by  the  formula  used  by  Mr.  W.  B. 
Bolton  exhibit  the  same  phenomena  in  a less  degree  than 
if  more  iodide  be  used.  The  formula  stands  thus  : — 


Ammonium  bromide 
Ammonium  iodide 
Ammonium  chloride 
Gelatine 
Water  ... 


60  grains 


5 

5 

10 

4 


5? 

?? 

55 

ounces 


Two  drops  of  hydrochloric  acid  (1  : 5)  are  added,  and 
then — 

Silver  nitrate  ...  ...  ...  120  grains 

Water  ...  ...  ...  ...  ounce 

Boiling  continued  for  half  an  hour. 

Another  excellent  formula  is  to  substitute,  for  the 
chloride  in  the  above,  15  more  grains  of  ammonium 

R 


242 


APPENDIX. 


iodide,  and  to  boil  for  one  and  a-half  to  two  hours.  The 
emulsion  will  be  sensitive,  and  exhibit  the  properties 
above  alluded  to.  In  both  cases  from  80  to  120  grains 
of  gelatine  must  be  added  (see  Chapter  XXXVII.)  after 
being  soaked  in  water. 

Warnerke1  s Modification  of  the  Emulsion  Process . — Mr. 
Leon  Warnerke  has  recently  found  that  the  image  pro- 
duced on  a gelatine  film  is  insoluble  in  hot  water  if  deve- 
loped by  pyrogallic  acid  (alkaline)  development.  A little 
study  of  the  question  will  show  that  in  the  half-tints 
there  must  remain  a soluble  portion,  which  will  be  next 
the  glass  plate,  and  this  cannot  be  removed*  without  re- 
moving the  whole  film.  Mr.  Warnerke  has  introduced  a 
paper  coated  with  gelatine,  from  which  the  film  can  be 
removed  by  transferring  it  to  glass  or  paper,  as  in  carbon 
printing.  The  soluble  matter  can  then  be  washed  away  by 
hot  water,  and  the  image  alone  will  remain  on  the  plate,  all 
the  transparent  parts  being  bare  glass.  This,  in  its  turn, 
can  be  re-transferred,  and  so  we  have  a perfect  process  in 
which  hyposulphite  need  never  be  used.  Amongst  other 
plans,  intensity  can  be  given  by  applying  permanganate 
to  the  film,  the  gelatine  causing  a deposition  of  manganic 
oxide. 

Methods  of  Packing  Plates . — The  method  of  packing 
adopted  by  some  dry-plate  makers  is  an  intolerable 
nuisance.  They  make  zig-zags  of  thick  paper,  which 
they  stuff  between  the  ends  of  each  plate,  or  pair  of 
plates ; and  when  a packet  is  unclosed  and  a plate  taken 
out,  there  is  an  endless  bewilderment  of  paper  and  glass, 
each  out  of  place  and  hard  to  put  right.  For  our  own 
part,  we  like  Mr.  England’s  plan.  He  uses  little  frames 
of  cardboard  to  place  between  his  plates,  and  they  are 
just  large  enough  to  be  flush  with  their  edges.  Thus,  for 
our  sized  plates  (7-|by  5)  we  cut  strips  of  card  3/16"  wide, 

inches  long,  and  an  equal  number  of  strips  5J"  long. 
Tough  bank-post  paper  is  gummed  over  with  stiff 
gum,  and  allowed  to  dry,  and  little  squares  of  about 


APPENDIX. 


243 


half-inch  size  cut  out.  A short  piece  and  a long  piece 
are  laid  together,  or  a pair  of  lines  ruled  at  right  angles 
to  one  another  on  a board,  and  when  the  square  of 
gummed  paper  is  made  to  adhere  beneath  them,  and 
then  deftly  folded  over,  two  sides  of  the  required  frame 


// 


were  made.  One  more  long,  and  one  more  short  piece, 
similarly  treated,  completed  the  frame.  Four-sheet  card  is 
what  Mr.  England  recommends.  When  the  strips  are 
cut,  we  make  about  thirty  of  these  frames  in  an  hour. 
The  plates  are  packed  alternately  back  to  back  and  face  to 
face,  in  the  latter  case  a frame  being  placed  between  them. 

Our  plates  are  packed  in  half-dozens,  enclosed  in  two 
thicknesses  of  orange  paper.  The  two  packets  are 
enclosed  in  pieces  of  black  varnished  paper,  and  then 
placed  in  boxes. 

Boxes  made  of  stiff  millboard,  and  covered  with  orange 
paper,  are  useful.  The  cover  should  cover  both  the  top 
and  sides  of  the  box.  They  should  not  be  too  small, 
but  be  1 inch  longer  and  ^-inch  wider,  inside  measure- 
ment, than  the  plates.  A depth  of  1-J  inches  will  then  take 
one  dozen  plates.  Some  makers  pack  plates  with  a mere 
sheet  of  pure  and  napless  paper  between  the  two  films. 
If  the  plates  are  really  flat,  this  plan  may  be  adopted,  but 
then  the  plates  must  be  flat,  otherwise  the  surfaces  are  apt 
to'get  scratched. 


244 


APPENDIX. 


Sensitometers. — A very  useful  piece  of  apparatus  sup- 
plied Tby  Marion  and  Co.  has  been  introduced  by  Mr. 
Warnerke  for  testing  dry  plates.  It  consists  of  a piece 
of  glass  covered  with  squares  of  different  thicknesses  of 
pigmented  gelatine,  each  square  carrying  a number  which 
corresponds  to  the  thickness.  The  illumination  of  the 
plate  is  made  by  a phosphorescent  tablet,  which  is  ren- 
dered luminous  by  burning  a small  piece  of  magnesium 
ribbon  immediately  before  use.  F ull  directions  are  issued 
with  these  sensitometers.  If  a plate  be  exposed  it  will 
show  on  development  a certain  number.  These  numbers, 
when  read  on  a scale,  will  show  the  relative  sensitiveness 
of  the  two  plates.  By  using  a sensitometer  with  the 
same  batch  of  plates,  experiments  on  developers  can  be 
well  undertaken.  As  a guide,  we  may  state  that  on  this 
standard  sensitometer,  if  the  number  14  is  shown  on  deve- 
lopment, the  plate  is  slow ; if  18,  fairly  rapid ; if  21, 
rapid ; and  if  25,  very  rapid.  A wet  plate  shows,  as  a rule, 
the  numbers  4 to  6.  Each  number  shows  an  addition  in 
sensitiveness  of  about  one-third  of  the  preceding  number. 
Plates  prepared  according  to  Chapter  XXVII.  should 
show  the  number  25  if  kept  two  days  after  washing. 

Another  ingenious  sensitometer  has  lately  been  brought 
out  by  Messrs.  Mucklow  and  Spurge,  and  consists  of  a 
series  of  chambers  which  are  illuminated  by  different 
sized  orifices,  the  area  of  each  bearing  some  constant 
ratio  to  each  other. 

Kit  for  Developing  on  Jour. — A small  chemical  chest  is 
a luxury  on  tour,  but  not  requisite.  All  that  is  absolutely 
necessary  for  developing,  besides  a screen  for  the  candle, 

is — 

G-oz.  bottle  of  concentrated  pyrogallic  acid. 

G-oz.  „ „ ammonia  and  bromide. 

|-lb.  of  alum. 

1 lb.  of  hyposulphite. 

2 oz.  of  a 20-grain  solution  of  potassium  bromide. 

2 oz.  of  a 25  per  cent,  solution  of  ammonia. 


APPENDIX. 


245 


2 oz.  glycerine  (useful  also  for  sun  burns). 

1 oz.  of  pyrogallic. 

1 oz.  measure. 

1 drachm  measure. 

6 trays. 

Small  ball  of  string. 

A sponge. 

A duster. 

Gummed  paper. 

All  the  above  may  be  packed  in  a very  small  box,  and 
\ lb.  of  ferrous  sulphate  and  1 lb.  of  neutral  potassium 
oxalate  may  be  taken  in  addition.  A box  10  inches  long, 
7 inches  wide,  and  7 deep  will  hold  all  of  these.  Now, 
all  the  foregoing,  camera  included,  can  be  packed  in  a 
small  basket  about  18  inches  long  by  a foot  wide  and 
15  inches  deep  ; and  it  will  be  found  that  no  damage  of 
any  kind  will  happen  to  either  plates  or  bottles,  so  long 
as  they  are  fairly  tightly  packed.  The  wicker  acts  as  a 
spring  when  porters  fling  the  baggage  about,  as  is  always 
the  case.  Our  strong  advice  is,  always  to  pack  your  photo- 
graphic kit  in  a basket.  This  basket  dodge  belongs  to  Mr. 
England — at  least,  he  first  pointed  out  its  advantages,  and 
he  invariably  adopts  it.  A two-foot  square  of  india- 
rubber  sheeting  is  useful  during  development  to  save 
messes  on  the  table,  and  is  utilized  in  packing  to  wrap 
round  the  boxes  of  plates  to  prevent  any  rain  or  dust  pene- 
trating to  them  during  transit. 

7 rays. — As  regards  the  trays,  we  believe  that  tin  trays 
lined  with  india-rubber  sheeting,  as  adopted  by  Mr. 
England,  would  be  better  than  anything  else.  Failing 
these,  we  would  recommend  ebonite,  but  their  exposure 
to  the  sun  should  be  avoided,  since  they  will  soften  and 
flatten  out.  Another  tray  is  made  by  turning  up  the 
edges  of  ferrotype  plates  and  bending  round  the  corners. 
These  are  cheap,  and  last  some  time. 

Ordinary  papier  mache  trays  will  answer,  but  with  alka- 
line development  the  varnish  is  apt  to  dissolve. 


APPENDIX. 


246 

Porcelain  dishes  are  usually  too  uneven  in  their  bottoms 
to  be  economical. 

Keeping  Gelatine  Emulsion . — When  a gelatine  emulsion 
has  been  prepared  for  use,  and  has  set,  it  may  be  kept  an 
unlimited  time  by  cutting  it  into  lumps  of  (say)  half  an 
inch  wide,  and  allowing  it  to  stand  in  alcohol ; or,  after 
setting  in  a flask  or  jar,  the  alcohol  may  simply  be  poured 
on  it,  and  it  will  keep  free  from  all  decomposition.  When 
required  for  use,  the  alcohol  is  poured  off,  and  the  jelly 
melted  in  the  ordinary  manner. 

Increasing  the  Sensitiveness  of  Gelatine  Plates  by  Silver 
Nitrate. — Dr.  Eder  and  Captain  Toth  have  found  the 
following  plan  to  answer  of  using  silver  nitrate  with 
gelatine  plates.  After  the  plates  are  prepared  and  dried  in 
the  usual  way,  they  are  laid  for  from  three  to  five  minutes 
in  the  following  solution,  which  must  be  thoroughly 
Altered : — 

Alcohol  ...  ...  ...  12  ounces 

Silver  citrate  solution  ...  1 dr. 

The  silver  citrate*solution  is  made  as  follows  : — 

Silver  nitrate  ...  ...  ...  50  grains 

Citric  acid  50  „ 

Water 1 ounce 

The  plates  are  placed  on  blotting-paper  in  a place 
perfectly  free  from  dustj  and  allowed  to  dry,  which  they 
do  in  a few  minutes.  The  plates  are  developed  by  any 
of  the  ordinary  developers.  The  sensitiveness  is  increased 
three-fold  according  to  the  above  experimenters. 

Note-Book  for  Registering  Plates. — In  making  an  expe- 
dition during  which  plates  cannot  be  developed,  or 
when  only  some  can,  it  is  advisable  to  enter  in  a note- 
book ail  details.  We  give  an  extract  from  a note- 
book, which  will  show  the  form  we  recommend.  It 
must  be  premised,  however,  that  each  plate,  besides 
bearing  the  number  of  the  batch,  should  also  bear  a dis- 
tinctive number,  which,  for  convenience,  may  be  written  on 
the  same  label  as  that  indicating  the  batch,  but  using  a red 
pencil  instead  of  blue. 


Remarks. 

Use  of  bromide 
required  in  de- 
veloping. 

Detail  in  dark 
trees  of  island 
fairly  out. 

Hypo,  used  in 
developer. 
Detail  fair. 

•I9d0I9A9Q; 

o o o 

Pm  Eh 

•podopA9a 

20/6/81 

20/6/81 

20/6/81 

Subject. 

River  Arun, 
looking  to- 
wards mill. 

Lake  near  Ar- 
undel, from 
south. 

j 

Same  as  13. 

•amsodxg; 

10  sec. 

Inst. 

3 -inch 
opening 

30 

CO  co  | | | <M 

'SU9T; 

* _l_  * 

g § 1 1 1 g 

jo  aeqmn^i 

CO  »C  O 1— t <M 

*— * w rH  r-l  CO  CO 

•joqm  njq 

J9  J9UXO  JIS  U9  g 

26 

26 

26 

26 

18 

18 

•qojna; 

98 

98 

98 

98 

82 

82 

•9PHS 

CO  tO  CO  t>-  CO 

G 

Cloudy 

G 

•anon 

2.30 

3.10 

2.35 

•a^a  j 

18/6/81 

)) 

18/6/81 

WA  means  Dallmeyer’s  wide-angle  landscape  lens.  t HR  means  Dallmeyer’s  rapid  rectilinear  lens. 


248 


APPENDIX. 


When  the  slides  are  filled  before  starting,  the  columns 
filled  up  are  4,  5,  6,  7,  and  the  rest  are  filled  up  after 
exposure  and  after  development.  By  adopting  this  plan, 
a complete  record  of  every  plate  exposed  and  developed  is 
obtained,  and  will  be  found  of  use  in  judging  of  exposures. 

Sulphite  of  Soda  in  the  Alkaline  Developer. — At  page  199 
it  was  mentioned  that  Mr.  Berkeley  had  recommended 
the  use  of  sulphite  of  soda  with  pyrogallic  acid.  The 
most  recent  formula  given  by  that  gentleman  is  as 
follows  : — 200  grains  of  sodium  sulphite  are  first  dissolved 
in  1 ounce  of  water.  When  the  crystals  are  dissolved  the 
solution  is  neutralized  by  adding  a strong  solution  of 
citric  acid  (about  4 grains  of  citric  acid  generally  suffices)  ; 
50  grains  of  pyrogallic  acid  are  then  added.  This  is 
about  a 10  per  cent,  solution  of  pyrogallic  acid,  and  corre- 
sponds with  formula  P,  page  191,  for  which  it  may  be  sub- 
stituted. The  solution  will  remain  colourless  for  months, 
and  paper  enlargements  may  be  developed  by  using  it 
without  leaving  any  stain.  It  is  an  excellent  formula. 

Dr.  Lohsds  Preparation  of  Pure  Silver  Bromide  without 
Washing. — Dr.  Lohse  prepares  silver  bromide  in  the  usual 
manner,  and  after  boiling,  and  before  adding  the  addi- 
tional gelatine,  adds  acetic  acid  to  the  emulsion.  Every 
100  grains  of  gelatine  used  before  boiling  requires  about 
1|-  ounces  of  acetic  acid.  The  emulsion  is  then  diluted 
with  20  volumes  of  water,  and  allowed  to  settle  three  or 
four  days.  The  bromide  settles,  and  the  supernatant  liquid 
may  be  drawn  off.  To  every  100  grains  of  silver  nitrate 
originally  used  100  grains  of  gelatine  should  be  weighed 
out,  swelled,  and  dissolved  in  3J  ounces  of  water.  The 
bromide  is  then  added  and  incorporated  by  shaking  in  a 
bottle.  The  sensitiveness  seems  to  be  impaired  to  a cer- 
tain extent  by  this  mode  of  proceeding ; but  the  plates 
are  bright,  dense,  and  clear. 

Erratum. — Page  6,  3rd  paragraph,  line  15,  should  read : — “ Thus  he 
found  1 grain  of  the  following  bromides  to  require  annexed  number  of 
grains  of  silver  nitrate.” 


Piper  & Carter,  Printers,  5,  Castle  Street,  Holborn,  E.C, 


To  ^TtotograyThers,  Crayon,  Jlr- 
tists , Wetter  Color  jlrtists , 
Portrait  Painters , Workers 
lit  Pctstel , Crayons , artcL 

Amatenrs. 

It  will  pay  you  to  write  for  my  new  reduced 
price  list  of  Photographic  Stock  and  Artists’ 
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When  you  write  for  it  please  inform  me  what 
branch  of  the  business  you  are  now  engaged  in. 
In  making  prices,  I have  endeavored  to  recollect 
that  low  prices  for  good  goods  make  the  best 
advertisement  any  business  man  can  have. 

Hoping  to  hear  from  every  artist  in  the 
United  States  and  Canada  who  has  not  already 
received  it,  I remain 

Yours  truly, 

W.  E.  EEID, 

Manufacturer,  Importer,  and  Jobber  of  Pine  Art  Goods  of  all  kinds, 
352  & 354  Euclid  Avenue, 

Cleveland,  Ohio. 


I 


And  those  contemplating  the  Study  of 


PHOTOGRAPHY 


should  bear  in  mind  that  we  are  anxious  to  send  them  our  new 
Illustrated 


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An  idea  of  our  Stock  may  be  gathered  from  the  Catalogue.  We 
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Address 


II 


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-ESTABLISHED  1865.— 


Wm.  D.  H.  Wilson. 


WILSON,  HOOD  & CO., 

Wo.  825  Arch  Street,  Philadelphia, 

Solicit  your  orders  for  Lenses,  Camera  Boxes,  Chemicals,  Plates, 
&c.,  needed  in  working 

®M  A\l»  WET  PLATES. 

WE  CAN  FURNISH 

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Boss,  Steinheil,  Enryscope,  Morrison,  or  any  other  make  of  Lenses. 
Carbutt’s,  Eastman’s,  or  Cramer  & Borden  Dry  Plates. 

Lamps,  Printing  Frames,  Paper,  &c. 

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THE  FOLLOWING  ARE  OUR  MOST  DESIRABLE 

DRY  PLATE  OUTFITS- 


“W.  H.  C.”  Outfit  “A.”  $10.00. 

1 Am.  Op.  Co.  Ebonized  4x5  Box, 

1 “ “ Double  Dry  Plate  Holder, 

1 Tripod, 

1 Waterbury  Achromatic  Lens, 

1 Carrying  Case. 

Extra  Double  D.  P.  Holders,  each,  $2.70. 
Separately,  prices  as  follows  : Camera  Box 
and  Holder,  $7.25  ; Tripod,  $2.40  ; Lens,  $3.00. 
Box  has  7 inch  draw.  This  outfit  with  a 1-4 
C.  S.  Portrait  Lens,  $18. 

“W.  H.  C.”  Outfit  “ E.”  $2150. 

1 4x5  Am.  Op.  Co.  Folding  Mahogany  Box, 

1 “ ! “ Patent  Double  D.  P.  Holder, 

1 Tripod, 

1 Carrying  Case. 

Extra  Patent  Double  D.  P.  Holders,  each 
$2.70. 

Lenses  for  above  Outfit. 

For  Views.— 1-4  Darlot  View  Lens,  $5.50 ; 
4.5  Ross  Rapid  Symmetrical  Lens,  $30.00.  For 
Portraits,  Animals,  Etc.— No.  2 Ross  C.  D.  V. 
Lens,  $50.00.  Box  has  8 1-2  inch  draw. 

“W.  H.  C.”  Outfit  “F.”  $12.00. 

1 5x8  Am.  Op.  Co.  Ebonized  View  Box, 

1 “ Patent  Double  Dry  Plate  Holder, 

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Complete  Price  List  Free  by  Mail. 


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Separately,  prices  as  follows  : Camera  Box 
and  Holder,  $8.50  ; Tripod,  $2.40  ; Lens,  $5.40. 
Box  has  8 inch  draw. 

“ W.  H.  0."  Outfit  “ G.”  $18.50. 

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Extra  Double  Dry  Plate  Holders,  each,  $4.00. 

Separately,  prices  as  follows  : Camera  Box 
and  Holder,  $9.75  ; Tripod,  2.40  ; Lens,  $5.40. 
Pair  Lenses,  $6.00.  Box  has  8 inch  draw. 

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Extra  Double  Dry  Plate  Holders,  each,  $4.00. 
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For  Lenses  suitable  for  above,  see  Lens 
List.  We  advise  a pair  of  4x5  Ross’  Rapid 
Symmetricals,  $61.00,  with  a No.  4 Ross’  Port- 
able Symmetrical  Lens  at  $30.00,  or  a No.  5 
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use  on  a 5x8  plate. 

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Ill 


What  is  Said  hy  the  Readers  of 


PHOTOGRAPHICS. 


We  cannot  recommend  it  too  highly  to  our  colleagues. — Leon  Vidal,  Editor  of 
the  Paris  Moniteur. 

Among  the  photographic  writers  of  America,  E.  L.  Wilson  stands  without  a 
compeer,  and  he  once  more  claims  our  thanks  and  admiration  by  his  excel- 
lent work.  Photographics.— Dr.  H.  Vogel,  Berlin. 

By  far  the  best  photographic  book  ever  published  in  America.  It  is  written 
with  great  elegance  ancl  masterly  handling  of  the  subject,  and  it  is  very  com- 
prehensible.— Dr.  E.  Horning,  Editor  of  Photo.  Correspondenz,  Vienna. 

Photographics  is  the  most  imposing  book  devoted  to  photography  I have 
ever  seen.— J.  F.  Ryder,  Cleveland. 

Photographics  looks  fine  and  is  selling  well.  We  are  doing  our  best  to  push 
it.— W.  Irving  Adams,  New  York. 

The  plan  of  the  book  is  novel.  . . . Mr.  Wilson  could  hardly  fail  by  his 

plan  in  making  a useful  and  practical  publication.— Anthony's  Bulletin , New 
York. 

We  have  no  hesitation  in  saying  that  Wilson’s  Photographics  is  an  element- 
ary masterpiece  from  which  all  cannot  fail  to  obtain  a vast  quantity  of  infor- 
mation.— Dr.  R.  Sheldon  Mackenzie,  Editor  Philadelphia  Evening  News. 

I have  inquiries  for  a good  book  on  photography,  and  I think  3rours  is  that 
book.— John  Carbittt,  Philadelphia. 

It  is  a complete  library.— W.  D.  Gatchel,  Cincinnati,  O. 

We  know  of  no  one  in  our  fraternity  more  capable  of  compiling  such  a work 
for  the  benefit  of  the  photographic  brotherhood  than  Mr.  Wilson. — J.  H.  Fitz- 
gibbon,  in  St.  Louis  Practical  Photographer. 

This  valuable  and  suggestive  book  is  without  any  doubt  the  greatest  effort  yet 
made  by  its  author.  It  demands  a position  in  the  library  of  every  photographer, 
and  this  position  it  will  assuredly  attain  as  soon  as  its  merits  become  known. 
— Editor  Photographic  Times  and  American  Photographer. 

Photographics  hits  the  nail  right  on  the  head.  I would  rather  have  it  than 
all  the  other  books  on  photography  put  together.  The  idea  is  capital,  as  it  is 
original,  and  gives  us  the  whole  thing  in  a nutshell. — B.  W.  Kilburn,  Littleton, 

I hope  that  every  photographer  will  see  to  it  that  his  $4  goes  direct  to  you , 
without  any  dealer’s  commission  off,  in  order  that  you  may  have  the  full  ben- 
efit of  its  price — a benefit  indeed  for  the  many  years  you  have  played  your  part 
so  carefully  upon  the  photographic  stage  for  us.— Fred.  C.  Phillips,  St. 
Thomas. 

It  is  the  most  unique  and  powerful  work  upon  the  subject  I have  ever  seen. 
I hope  that  you  will  live  to  gather  and  enjoy  much  fruit  from  the  tree  you  have 
helped  to  plant  and  so  carefully  nurtured.— J.  E.  Beebe,  Chicago. 

The  Second  Thousand  is  now  in  Press.  “ It  is  a whole  Library.” 


GET  WILSON’S  PHOTOGRAPHICS. 


Will  be  mailed,  post  paid  to  any  address,  on  receipt 
of  $4.00. 


Benj 


H 


RENCH  & CO, 

319  Washington  Street, 

BOSTON, 


Sole  Agents  in  the  United  States  for  the  Celebrated 

V OIGTLANDER  & SON 


Portrait  Lenses, 

— AND  THE  — 

WONDERFUL  EURYSCOPE, 


THE  BEST  LENSES  EVER  MADE. 

— ®p»TRY  THEM 

DAHLOT’S  aidTiew  LENSES. 


All  Genuine  Darlots  have  B.  F.  & Co.  engraved 
on  Tube. 


Illustrated  Catalogue  Sent  on  Application. 


STANDARD 

Photographic  Literature. 

SCOVILL’S  PHOTO.  SERIES. 

No.  I.  THE  PHOTOGRAPHIC  AMATEUR, 

By  J.  Traill  Taylor. 

A Guide  to  the  Young  Photographer,  either  Professional  or  Amateur. 

Price,  50  Cents. 

No.  2.  THE  ART  AND  PRACTICE  OP  SILVER  PRINTING, 

By  H.  P.  -Robinson  and  Capt.  Abney,  R.  E.,  F.  R.  S. 

Price,  50  Cents  (illuminated  Cover),  Cloth  Bound,  75  Cents. 

No.  3.  The  British  Journal  Photographic  Almanac  for  1882,  as  Vol.  I., 

AND 

THE  PHOTO.  NEWS  YEAE  BOOK  POE  1882,  AS  VOL.  II. 

Price,  75  Cents  for  the  Two  Volumes. 

Just  Out!  Just  Out!  Just  Out! 

3,500  Sold.  3,500  Sold.  3,500  Sold. 

No.  4.  HOW  TO  MAKE  PICTURES, 

The  A B C of  Dry  Plate  Photography , 

By  Henry  Clay  Price. 

Price,  Illuminated  Cover,  - 50  Cents. 

“ Cloth  “ - 75  “ 

No.  5— IS  IN  THE  BINDERY. 


SCOVILL  MANUFG-  00.,  Publishers. 


LIGHT  IN  THE  DARK  ROOM.  4* 

SAVE  YOUR  EYESIGHT  BY  USING 

CARBUTT’S 

Muitum  in  Parvo 

Dry  Plate  Lantern. 


(Patented  April  26,  1882.) 


Lantern  arranged  for  making  positives  by  contact. 


The  following  are  some  of  the  advantages  possessed  by  this  Lan- 
tern : It  is  simple  and  easy  to  manage,  nothing  complicated,  yet  has 
three  separate  and  distinct  forms  of  light.  It  is  adapted  for  the  use 
of  either  oil  or  gas  ; is  about  nine  inches  square  by  fourteen  high, 
with  8x10  deep  ruby  glass  in  front.  Each  Lantern  is  provided  with 
a coal-oil  lamp,  with  improved  patent  burner,  and  silvered  reflector, 
which  may  be  revolved  in  any  direction,  and  operated  from  the  out- 
side. By  removing  the  revolving  lamp  bed,  a hole  will  be  found 
through  which  a gas  burner  can  be  introduced. 

It  can  be  used  for  seven  or  more  different  operations  in  photography, 
several  of  which  have  never  been  combined  in  any  one  lantern,  to  wit : 

1.  A safe  light  for  the  preparation  of  gelatino-bromide  emulsion. 

2.  A safe  light  for  the  coating  of  gelatino-bromide  plates. 

3.  A safe  light  for  developing  the  most  sensitive  plates,  while  for 
preparing  developer  or  doing  other  work,  the  room  can  be  instantly 

VII 


flooded  with  white  light  and  as  quickly  changed  to  the  red,  giving 
abundance  of  light  by  which  to  develop  the  largest  sized  plates  used. 
The  adjustable  hood  effectually  shields  the  eyes  from  the  glare  of  the 
red  light,  a matter  of  the  greatest  importance  to  those  having  a large 
number  of  negatives  to  develop,  or  other  work  to  perform  necessi- 
tating red  light. 

4.  An  opal  light  by  which  to  examine  negatives  or  positives  after 
fixing,  enabling  the  operator  to  judge  of  their  quality,  thereby  avoid- 
ing the  necessity  of  leaving  the  dark  room  in  search  of  white  light. 

5.  A clear,  transparent  light  for  making  positives  on  glass  (gelatino- 
bromide).  This  feature  is  a valuable  one.  Any  photographer  can 
materially  add  to  his  revenue  by  making  these  most  beautiful  prod- 
ucts of  photography. 

6.  The  making  of  enlarged  negatives  from  gelatine  positives, 
placed  in  front  of  opal  light. 


Lantern  arranged  for  developing  and,  after  fixing, 
examining  negatives  by  opal  light. 


7.  The  making  of  photo-micrographs  with  the  clear,  transparent 
light,  which  can  readily  be  accomplished  with  the  gelatino-bromide 
plate  and  the  microscope. 

8.  By  the  adjustment  of  condensers  and  holder  for  slides,  and 
objective  in  front  of  the  clear  light,  a very  effective  magic  lantern  is 
formed. 

Price^  $6.00;  Boxed;  Ready  for  Shipment. 


Manufactured  and  for  sale  by 

JOHN  CARBUTT, 

628  and  630  Chestnut  St.,  PHILADELPHIA. 

Manufacturer  of  the  Celebrated  Keystone  Dry  Plates. 

VIII 


OR, 


EMULSION  PHOTOGRAPHY, 

By  Dr.  J.  M.  Eder,  the  eminent  German  Authority  on  Gelatine , etc ., 
translated  by  Mr.  Horace  Wilmer  and  edited  by  H.  Baden 
Pritchard,  F.  R.  S.,  editor  of  the  London  Photo.  News. 

NO  LIVING  AUTHOR 

has  made  such  a study  of  the  action  of  the  Haloid  Salts  of  Silver  in 
Emulsion  as  Dr.  Eder ; 

NO  LIVING  AUTHOR 

has  made  so  many  experiments  on  the  action  of  Gelatine  in  Emul- 
sions ; 

NO  LIVING  AUTHOR 

has  written  so  many  original  and  practical  notes  on  the  Gelatino- 
Bromide  Process  as  Dr.  Eder  ; therefore,  there  is  no  work  on  the 
subject  which  can 

C O JVL  IP  A.  R TC  WITH  IT. 

Consequently,  whoever  desires  to  become  informed  on  these  all- 
important  particulars  must  peruse  Dr.  Eder’s  work  on  EMULSION 
PHOTOGRAPHY. 

PRICE,  handsomely  bound  in  cloth,  only  $1.00. 

For  sale  by  E.  & H.  T.  Anthony  & Co.,  New  York,  and  all  Photo. 
Stock  Dealers. 

Also,  the  Best  and  only  Reliable 

DRY  PLATE  APPARATUS, 

Embodying  the  THORP  and  BARKER  PATENTS. 

Also,  the  Celebrated  DALLMEYER 

LENSES^ 

than  which  there  are  none  equal  in  the  World  ! 

And  Everything  Pertaining  to  the  Photo.  Art. 

A Book  of  Instructions  Free  with  each  Outfit. 

Send  for  Illustrated  Price  Lists  and  Circulars.  Address 

E.  & H.  T.  ANTHONY  & CO., 

591  Broadway , NEW  YORK 


IX 


| The  Beebe  Dry  Plate,  |j 

MANUFACTURED  BY 

The  Chicago  Dry  Plate  k M’f’g  Co., 

2228  Indiana  Avenue,  Chicago. 

These  standard  Plates  have  reached  their  present  high 
and  enviable  reputation  from  the  fact  that  they  are  tested 
daily,  in  the  most  thorough  and  careful  manner,  by  Mr. 
Beebe,  in  an  exacting  and  critical  studio  practice. 

The  practical  every-day  photographer  will  find  his  wants 
met  by  this  plate. 


Note  Reduction.  BRICE  LIST.  Note  Reduction. 


SIZE. 

PER  DOZ. 

SIZE. 

Per  doz. 

x 4i  inches 

$o  65 

6-£  x 8£  inches.... 

$2  40 

A X ^ “ 

0 OS 

8 

x 10 

< < 

3 60 

J 

X “ 

I OO 

10 

x 12 

< i 

5 20 

4^-  x 6{  

I 25 

11 

x 14 
x 17 

X 20 

< < 

6 80 

c x 6 “ 

I ye 

*4. 

17 

18 

< < 

10  00 

c x 7 “ 

I 65 

i i 

17  c.O 

5^x7  “ 

I 75 

X 22 

< < 

20  OO 

5 x 8 “ 

1 85 

20 

x 24 

i i 

Complete  Formula  for  use  inclosed  in  each  Package. 


For  Sale  by  all  Healers. 

x 


On  and  after  May  1st , the  price  list  of 


JOHN  CAUBUTT’S 

“ KEYSTONE  ” 

Bromo-Gelatine  Ory  Plates 

WILL  BE  AS  FOLLOWS  : 


PRICE  PER  DOZEN. 


Size. 

A.&B. 

J.  C.  B. 

Size. 

A.&B. 

J.  C.  B. 

3£  x 4£  inches 

$0  65 

$0  72 

8 x 10  inches 

$3  60 

$4  00 

4x5  “ 

0 95 

1 04 

10x12  “ 

5 20 

5 80 

4£x5£  “ . ... 

1 00 

1 12 

11x14  “ 

6 80 

7 60 

4£x6*  “ 

1 25 

1 40 

14  x 17  “ 

10  00 

11  00 

5x7  “ 

1 68 

1 85 

17  x 20  “ 

16  00 

18  00 

5x8  “ 

1 80 

2 00 

18  x 22  “ 

18  00 

20  00 

6|  x 8±  “ 

2 40 

2 70 

20x24  “ 

22  50 

25  00 

7x9  “ 

3 00 

3 40 

Double-thick  Glass  used  on  all  sixes  above  11x14. 


Packed  in  light-tight  boxes.  Full  instructions  for  development 
accompany  each  package  of  plates. 


SUPPLIED  BY  THE 

SCOVILL  MAJfFG  COM  l'A\  Y 

And  all  Photo.  Stock  Dealers. 


XI 


«JTHE  ATTENTIONS 


m 


OF 


ip 


HOTOGRAPHERS  is  respectfully  called  to  the 


latest  issue  in 


and  a trial  of  our  New  Brand, 

THE  “MOUND  CITY,” 

solicited.  We  recommend  them  as  equal  to  any  yet  intro- 
duced. They  have  the  undoubted  and  hearty  indorsement 
of  hundreds  of  first-class  Photographers. 

In  point  of  reliability  and  uniformity  they  are  unex- 
celled ; develop  much  quicker  than  others,  and  are  about 
ten  times  as  sensitive  as  Wet  Plates. 

We  warrant  them,  and,  being  sold  at  the  following  reduced 
List,  must  meet  with  general  favor. 


PRESENT  PRICES. 


SIZE. 

3ix4| doz.  $0.65 

4 x 5 “ 0.95 

4ix5* “ 1.00 

4i  x 6£ “ 1.25 

5 x 7 “ 1.65 

5 x 8 “ 1.85 

6£x8£ “ 2.40 


SIZE. 

8x10 

doz.  $3. 

10x12 

“ 5. 

11  x 14 

“ 6. 

14  x 17 

“ 10. 

17  x,20 

“ 17. 

18  x 22 

“ 20. 

20  x 24 

“ 24. 

Ask  your  Dealer  for  them,  or  send  direct  to  us. 

Very  respectfully, 

H.  A.  HYATT,  Proprietor, 

St.  Louis,  Mo. 


XII 


8 8 § 8 8 8 S 


QAYTON  A.  DOUGLASS 


XIII 


REQUISITES  FOR 


EMULSION  MANUFACTURE. 


Thermometers,  Miami,  Flasks. 

GELATINE. — Nelson’s  No.  1,2  and  3;  Hen- 
derson’s; Coignet,  Swiss;  Heinrich,  Marde- 
burg  and  Nuremburg. 

Nitrate  Silver.  Bromide  Ammonium. 

SEND  FOR  PRICE  LIST. 


A COMPLETE  LINE  OF 

DRY  PLATE  OUTFITS 

AND  SUPPLIES. 

All  the  Standard  Brands  of 

DRY  PLATES. 

SEND  FOR  PRICE  LIST. 


DOUGLASS,  THOMPSON  & CO. 

XIV 


A NOVELTY. 


^Osborne’s  Patent  Pictrape  Forepids.^ 

These  form  a means  by  which  any  Photographer  may  produce  elaborate  and 
beautiful  balcony,  window,  doorway,  and  other  like  effects  in  portraiture, 
hitherto  only  obtained  by  the  use  of  elaborate  and  expensive  solid  wood  studio 
accessories.  The  effects  are  obtained  by  a very  simple  system  of  double  print- 
ing, thoroughly  explained.  The  closest  inspection  of  a photograph  obtained  in 
this  manner  fails  to  show  that  it  has  been  produced  otherwise  than  with  solid 
accessories,  while  the  price  is  so  low  as  to  put  them  within  the  reach  of  every 
one. 

The  Foreground  Negatives  are  made  to  suit  the  light  on  the  subject  from 
either  direction. 

PRICES  ARE  AS  FOLLOWS  : 

5 x 8,  Suitable  for  Cabinet  or  Promenade,  $2  OO 
6i  x 8\,  “ “ Boudoir,  - - 2 50 

8 x 10,  “ “ Bong  Panel,  - - 3 OO 

11  x 14,  “ “ Barge  Panels,  - 5 OO 

ALL  SIZES  CAN  BE  FURNISHED. 

Send  for  Circular,  which  is  accompanied  by  pictures  of  all 
styles  made. 

SCOVILL  MT’Gr  00.,  Trade  Agents. 

GS=FOR  SALE  BY  ALL  DEALERS. 

XV 


Most  Complete 
Assortment  in  the  W est 
of  A.  M.  Collins,  Son  & 

Co.’s  Card  Stock,  American 
Optical  Company’s  Apparatus, 
Supplies  for  the  Amateur.  Every- 
thing pertaining  to  the  Art  Photographic 
constantly  on  hand  at  Prices  that  cannot 
be  beaten  by  any  one.  Send  for  Price 
List,  and  give  me  a Trial  Order. 

N.  G.  THAYER, 


149  Wabash  Avenue , 

CHICAGO, 

ILL, 


XVI 


CZ^TH  K 

Philadelphia 

Photographer. 

Edward  L.  Wilson, 

Editor  and  Publisher, 

Philadelphia,  Pa. 

Subscription  Price, 

$5.00  per  Annum. 

Containing  all  of  the  Photo.  News,  both  Home  and 

Foreign. 


The  Photographic  Times 

AND 

AMERICAN  PHOTOGRAPHER. 

J.  TRAILL  TAYLOR,  Editor. 

Subscription,  $2  per  Annum. 

It  furnishes  all  the  latest  hints  for  practice. 

SCOVILL  MFG-.  CO,,  Publishers, 


NEW  YORK. 

XVII 


fcA 


GETTY  RESEARCH  INSTITUTE 

III  I 


3 3125  01059  3438 


°ORj\p\\\c 


NEW  YORK. 


419  & 421  Broome  St., 


SQOVILL  M F G GO. 


